* Copy light(-hires).css -> dark(-hires).css (with no changes yet)
* Add dark(-hires).css to makefile/qrc and show them in theme selector
* Dark theme (css part)
* Do not style unit selector in status bar via platform styles, use css instead
* No coloring via forms (*.ui)
* Implement and use helpers to style parts of rich text differently for light and dark themes
* Remove dark-hires due to #3217
* Revert changes to light-hires.css to avoid merge conflicts with #3217
- remove btc address length from address validator
- add an optional btc address check in validated line edit that defaults
to off and is used in GUIUtil::setupAddressWidget()
- an isAcceptable() check is added to validated line edit on focus out
which only kicks in, when a validator is used with that widget
- remove an isAcceptable() check from sendcoinsentry.cpp
- remove obsolete attributes from ui files, which are set by calling
GUIUtil::setupAddressWidget()
- move some more things to GUIUtil::setupAddressWidget() and remove them
from normal code e.g. placeholder text
