[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

src/qt/forms/signverifymessagedialog.ui

@@ -47,9 +47,6 @@
            <property name="toolTip">
             <string>The address to sign the message with (e.g. 1NS17iag9jJgTHD1VXjvLCEnZuQ3rJDE9L)</string>
            </property>
-           <property name="maxLength">
-            <number>34</number>
-           </property>
           </widget>
          </item>
          <item>
@@ -260,9 +257,6 @@
            <property name="toolTip">
             <string>The address the message was signed with (e.g. 1NS17iag9jJgTHD1VXjvLCEnZuQ3rJDE9L)</string>
            </property>
-           <property name="maxLength">
-            <number>34</number>
-           </property>
           </widget>
          </item>
          <item>