API: Use message-per-value for apihelp-query+revisions+base-param-prop

API: Use message-per-value for apihelp-query+revisions+base-param-prop

Use message-per-value for message
apihelp-query+revisions+base-param-prop to allow smaller strings
for translation and to add a parameter for the contentmodel for
prop=parsetree, as already done for action=parse&prop=parsetree.
Each prop in a message also will show up a new parameter on the help
page without the adjust of the translation (but than in english instead
of fully skip it).

Change-Id: I8aaa061cb59ec788f8f8e09e8088ba1064e3aa1e