[Qt] extend validate line edit and btc address validator

- 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