enhance translation possibilities in TransactionDesc / misc other changes

- remove "#include <QString>" as this is included in the header
- add some missing plural forms that can be translated
- change "yours" into "own address", which is easier to understand and translate in that context
- cleanup translatable strings to not include HTML or unneeded chars (e.g. ":")
- resize TransactionDescDialog a little (remove unwanted line-breaks with non english translations)

src/qt/forms/transactiondescdialog.ui

@@ -6,7 +6,7 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>600</width>
+    <width>620</width>
     <height>250</height>
    </rect>
   </property>