[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