Implementation of QEP 132:
Manage python cross-plugins dependencies
A new optional metadata entry will be added to metadata.txt: plugin_dependencies
The metadata will contain a comma separated list of plugin names, with a format similar
of the one used by pip, with optional version.
After a successful plugin installation, if the plugin has any unsatisfied dependency,
a dialog will pop-up with the list of unmet dependencies and the user
will be able to choose if she wants to install or upgrade the
dependencies or ignore them.
Example metadata:
plugin_dependencies = QuickMapServices==0.19.10.1,QuickWKT
Funded by GISCE-TI S.L.
