Better management of the different profiles: default, development, beta.

The 'development' profile has now a distinct ID: 
`info.febvre.Komikku.Devel`.

In the case of the 'beta' profile used for the Flathub beta branch, the 
data directory being shared, the database is named `komikku_beta.db`.

The icon `info.febvre.Komikku.Devel.svg` is now used with the 'beta' and 
'development' profiles.