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)