Improve message templates & Git environment support (easier pushing)

example new commitPageMsg:
pages/%fullpage% edit: %summary%%nl%%nl%Signed-Off-By: %user% <%mail%>%nl%X-DokuWiki-Page: %fullpage%

Example usage for envParams:
GIT_SSH=.../lib/plugins/gitbacked/bin/git-ssh-wrapper,SSH_PRIVKEY=.../dokuwiki-gitbacked-ssh-key.priv
Makes it much easier to push.