Add function to get all selected images

This should be used all over the code I guess instead of fiddling with
the db in many places.
Center filmstrip on first selected image in map mode

This fixes #9090
Revert "Add function to get all selected images"

This reverts commit 3ad2103f4dae9e935a0bc197d42f5fd595a4a757.
We should probably use the already existing dt_collection_get_selected
Add limit option to dt_collection_get_selected
Use dt_collection_get_selected with limit = 1
Update screenshots in apddata file
Announce changes to appdata format on devel list
Delete Sony thumbnail data
Merge remote-tracking branch 'upstream/master'
(Possibly) Fix drawing issue
Merge pull request #316 from naglak/master

Delete Sony thumbnail data
Merge pull request #317 from LebedevRI/draw-fix

(Possibly) Fix drawing issue
Merge remote-tracking branch 'upstream/master'
Fix some null pointer checks
l10n: updated ja.po by a3novy
wb_presets: Sony NEX-6 == Sony NEX-5R
wb_presets: Sony NEX-6 copy notice
Merge pull request #318 from LebedevRI/null-checks-0

Fix some null pointer checks
bauhaus: add a blinking non-intrusive cursor
Add parser/solver for mathematical formulas

Only trivial formulas are supported, like a simple calculator. Possible
operators are +-*/%^ and one variable, x or X, can be used. It also
supports increasing the variable with '++' and decreasing with '--'.