Create clean basis branch

[gizmecano]

Before considering any split from original upstream, try to set a clean basis branch is prerequite.

This branch should include main commits (integrated in official releases) but also various requests (considered as constructive or useful).

The cherry-picking method have to be preferred in order to sort correctly these changes.

• 172ce1e (cherry picked from commit ab08fe3)
• f2193b0 (cherry picked from commit f787646)
• c1c8910 (cherry picked from commit 01c7af0)
• afc4174 (cherry picked from commit ad64a97)
• f7fd4cd (cherry picked from commit c3bfb27) (proposed in Fixed logo link to use home URL getgrav/grav-theme-mediator#6)
• b2812e0 (cherry picked from commit ea75b8c) (considered in Move deferred javascript assets #3 and proposed in Move deferred javascript assets getgrav/grav-theme-mediator#20)