In flush mode load current theme private groups on login

[arnaud-morvan]

To keep things simple, I simply reload current theme when in flush mode and no default_theme for the user.
This have no impact on "not flush" mode.

[sbrunner]

It doesn't work in this case:

• Load theme Mixt
• Search for filtres
• Add data filtres

=> Groups: Filtres, Function OSM

• Login with demo

=> Groups: Private, Function OSM
Expected groups (Order?): Filtres, Function OSM, Private

[arnaud-morvan]

Note that this also occurs when there is a default_theme configured for the user.

[sbrunner]

Yes but it's wanted in the case of default_theme ...

[arnaud-morvan]

Should be better now, only add private first level group at end of layer tree. Finally not so complex.

[sbrunner]

For me it's OK, I let @fredj to have a third look :-)

[fredj]

LGTM, thanks