Bug 469862

SUMMARY
In Digikam it is possible to set the configuration location via a command line argument. This feature has many important uses and is only becoming more necessary (more about that below). I believe that it would be highly beneficial to expand this feature to the GUI. Digikam needs an option in the preferences window to create additional config files (called profiles) that can be selected during startup to use different configurations and databases.

**Note: I am not sure if this fits better under 'Setup-ConfigFiles', 'Setup-Database', or something else. Change as you see fit.

OBSERVED RESULT
- Config location can only be set using the command line arg.
- Multiple configs require you to manually create additional desktop entries with the desired config/database options if you want to launch them using the GUI
- Windows with different configs are all treated the same (they are not differentiated) so if you have multiple instances of Digikam open with separate configs, they stack in the taskbar and are treated as the same program. This is especially bad when you start opening dialogs and child windows of each instance.

EXPECTED RESULT
Profiles can be added, renamed, and removed in preferences. Optionally, a custom config location can be specified for each profile instead of Digikam assigning it a location. On boot, Digikam opens the default config file and reads a list of the added profiles. If there are no other profiles, it boots normally. If there are one or more profiles, it provides the user an option to select a profile to boot from (default, profileX, profileY, ...).

- The default config/profile stays in the same location as it is now (to maintain compatibility) and is the master config that Digikam always relies on to be there so it can fetch the rest of the profiles and config locations. (The only change to the default config is that it will contain a list of the additional profile names and config locations to call on when it initially boots).
- The default profile is whatever config is in the current default config location or the config location provided by the command-line argument. It can only be renamed or moved by using the command-line argument.
- If no custom config location is set for a profile, it will be located under "~/.config/digikam/<profileXYZ>" (or a similar location decided by the devs).
- Digikam windows will append the name of the active profile to the window name to differentiate them.
- Digikam windows of different profiles should be differentiated in such a way that they are not stacked together in the taskbar (but windows of the same profile and child windows/dialogs are stacked/treated the same).

ADDITIONAL INFORMATION
Multiple configs are particularly useful when you are using a remote database for multi-user support. If you are away from the local network you can't use Digikam without a VPN which is so slow that Digikam becomes unusable. Starting Digikam with a secondary config/database specifically for local collections (using the command line argument) allows you to use Digikam locally without a fast connection (or any connection) to the shared database. As more and more people have access to home NAS devices to host their photos and Digikam database, this issue only becomes more necessary to solve.

Additionally, multiple configs are useful in other situations such as allowing you to keep your private/local collections more separated from shared family ones, allowing multiple remote databases to be used (Ex: shared family NAS DB and shared work DB), and allowing separate behaviors for different needs (Ex: one config can be performance-oriented, while another can be focused on the highest quality screen rendering and most up to date image/metadata info syncing).

Because of all of these uses, I believe a GUI option for multiple configs is important to have.