fix Lintian and dpkg-gencontrol warnings

Fixed:
```
dpkg-gencontrol: warning: package libnemo-extension1: unused substitution variable ${misc:Pre-Depends}
dpkg-gencontrol: warning: Depends field of package libnemo-extension-dev: unknown substitution variable ${shlibs:Depends}
dpkg-gencontrol: warning: Depends field of package gir1.2-nemo-3.0: unknown substitution variable ${gir:Depends}
dpkg-gencontrol: warning: Depends field of package gir1.2-nemo-3.0: unknown substitution variable ${shlibs:Depends}

W: nemo source: ancient-standards-version 3.9.2 (current is 3.9.5)
E: nemo source: not-binnmuable-any-depends-all nemo -> nemo-data
E: nemo-data: python-script-but-no-python-dep usr/share/nemo/actions/myaction.py
```

Overridden:
`W: nemo: menu-icon-missing usr/share/pixmaps/nemo.xpm`