* fix Sphinx 1.6 compatibility leading to the "tiles" on the home page
not working anymore: 1.6 replaces BuildEnvironment.reolve_toctree by
TocTree().resolve(), while the method still exists it's not actually
called anymore
* rejigger some CSS as the second section went from one big tile to 3
smaller tiles, and got laid out as a row rather than a second 2x2
block. Recode the entire mess with flexbox, remove some stuff which
conflicted with boostrap (this screen should probably be
de-boostrapped and completely converted to flexbox or grid)
* add building CSS from LESS to the makefile, all Odoo devs should
have less installed locally (for assets)
Pretty much completely rewritten theme with custom HTML translator and a
few parts of the old theme extracted to their own extensions.
Banner images thought not to be that huge after all, and not worth the
hassle of them living in a different repository.
co-authored with @stefanorigano
Xavier Morel