[Qt] extend validate line edit and btc address validator

- added minimum address length to validator and fixed maximum length (was
  35, but addresses are at maximum 34 chars long)
- an address < minimum address length is considered intermediate in the
  validator
- 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 unneeded attributes from ui files, which are set by calling
  GUIUtil::setupAddressWidget()