First batch of high DPI fixes

Soem small things like the triangles in our custom dr widgets are still
missing, but the big issues should be solved now.
I only tested these thigns by setting the screen DPI using xrandr, I am
not 100% sure if that is a perfect simulation.
People using a high DPI screen should still set the panel_width in the
config to something bigger.
Fix libpng-1.4 build
fix several translating errors
fix base curve mismatching
update chinese translation
Merge pull request #555 from cherrot/i18n_zh_CN

I18N: Update Chinese translations. Fix several translating errors
High DPI: More fixes, this time cairo stuff

TODO:
 - color picker
 - masks
 - anything else?
Lens IOP: add autodetection, based on fact "did user or did not changed anything in GUI from autodetected values"
Lens IOP: fix 2->4 migration
Fix lens iop when applied "automatic preset" and changed something in gui when lens data is missing in exif
Some small fixes
Outdated
Fixes