Do not unset/overwrite system environment CFLAGS/LDFLAGS

From hasufell on IRC
Merge pull request #547 from dorkster/bugfixes

Do not unset/overwrite system environment CFLAGS/LDFLAGS
Update to version 0.18
Fix clang bug in CMakeLists.txt

Courtesy of hasufell
Update flare.desktop.in

Translate the desktop file in both french and german
Merge pull request #548 from cjsthompson/master

Translate the desktop file in both french and german
Little changes in translation
Merge pull request #553 from Pawonashi/patch-5

Little changes in translation