Improve filter on import

Instead of showing all images, we set the filter to the smaller of the
default import rating and the current filter. This ensures that the
imported images are shown, but that we don't reduce the filter
unnecessarily.
Update comments for improved import filter handling
Keep old import filter reset for collect operations
A few new strings
updated translation
Merge remote-tracking branch 'upstream/master'
Merge branch 'purge-unused-tags' of https://github.com/darktable-org/darktable
highlights: be less aggressive.

works fine for my single test shot. more testing would be great (+opencl version pending)
Merge remote-tracking branch 'upstream/master'
GND show the line correctly if orientation is on
Merge remote-tracking branch 'upstream/master'
CR show keystone line correctly if orientation is on
Merge remote-tracking branch 'upstream/master'
Fix return value of dt_conf_get_int64 to be int64_t

No harm done, this function isn't used anywhere yet.
Use dt_conf_get_int64 to read cache_memory
Extend the upper limit for the cache size to 4Gb.

This will let dt cache around 131000 compressed thumbnails.
Fix support for uint32_t value in preferences.
Merge pull request #300 from darktable-org/extend-cache-upper-limit

Extend the upper limit for the cache size to 4Gb.
Revert "Fix support for uint32_t value in preferences."

This reverts commit a2048b8e8cb062748129277d29b98af126887569.

This "fix" is bogus and probably does the opposite of what was intended.
And it breaks intended behaviour.
Make magic constant (4gb) more readable