usefull manpages for owncloud and mirall

* replaces the generated manpages form sphinx by to extra ones, that are more manpage style. Nobody wants to have the complete guide in a manpage.

* adding --monoicons option to usage.rst

Closes: Issue #183 "oc-623 - [desktop client] no man page"

additional dependencies:
 * asciidoc

but ocsync also needs this package.