Humble App support

[UncleGoogle]

Closes #169 Closes #170 (the only missing thing is list of humble collection games when humble App is not installed locally)

I've tried to implement also getting last played times, but apparently Galaxy does not imports game times for subscription games.The workaround would be to return humbleapp games as regular owned games.

For now I rejected this idea as their presence rely on humbleapp client installed (so in case of having to plugin installed - one one machine with installed humbleapp client -- second one on the machine w/o it - would produce infinite conflict on GOG backends). Subcription games interface is free of this problem as I can raise error instead of returning empty list of games, and then Galaxy does not remove them from user library.

[lgtm-com[bot]]

This pull request fixes 1 alert when merging ec813d5492f1b9b5b8d4f299a2561619ac84534c into eb17cfac34f2ed380742a8ad54a46fdc92ad1d6c - view on LGTM.com

fixed alerts:

• 1 for Unused import

[lgtm-com[bot]]

This pull request fixes 1 alert when merging 417b18481beb780d5d52dbc365790088744eb8b9 into eb17cfac34f2ed380742a8ad54a46fdc92ad1d6c - view on LGTM.com

fixed alerts:

• 1 for Unused import

[lgtm-com[bot]]

This pull request fixes 1 alert when merging 6ba55d454157c9a551e08b9ef9c3f997622e61e1 into eb17cfac34f2ed380742a8ad54a46fdc92ad1d6c - view on LGTM.com

fixed alerts:

• 1 for Unused import

[lgtm-com[bot]]

This pull request fixes 1 alert when merging 9d9995b67b31e414b76f77a8a258fca026146fcc into eb17cfac34f2ed380742a8ad54a46fdc92ad1d6c - view on LGTM.com

fixed alerts:

• 1 for Unused import