Fixing dependencies for Google plugin

[theute]

At least this change was required on my machine running on Fedora 29...

[psss]

We should probably add python2-google-api-client to Requires. But it brings a bunch of new dependencies:

cairo
cairo-gobject
fontconfig
libX11
libX11-common
python2-gobject-base
dejavu-fonts-common
dejavu-sans-fonts
fontpackages-filesystem
libXau
libXext
libXrender
libxcb
pixman
python2-SecretStorage
python2-asn1crypto
python2-cairo
python2-cffi
python2-configparser
python2-cryptography
python2-dbus
python2-entrypoints
python2-fasteners
python2-gflags
python2-httplib2
python2-keyring
python2-monotonic
python2-oauth2client
python2-ply
python2-pyOpenSSL
python2-pyasn1
python2-pyasn1-modules
python2-pycparser
python2-rsa
python2-uritemplate
python2-xpyb

Not sure. We could also break did into several subpackages to prevent fetching too much dependencies for those who are not interested in all plugins. Or use dnf's weak dependencies? For pip this works very nicely:

pip install did[google]

Is something like this possible with dnf? Any recommendations?

[csams]

@psss This kind of à la carte plugin selection is what I had in mind with #160. The loader there supports plain file system paths but also "foo.bar.baz" identifiers for modules anywhere on the python path. You could publish some plugins on pypi and just have users pip install --user did-theplugin if they want them.

[psss]

That sounds good, @csams. Thanks for the idea. We can do the plugin cleanup/separation later. For now, let's at least update the documentation.