Installation guide for HA.
(cherry picked from commit 19661ce0bd1fd0a773ca23d996f9c2ba8ea6f1b2)
Fixing HA layout
(cherry picked from commit 7f1af8e0b28cad277e52ebde07283c4832fb564b)
Fixing HA layout.
(cherry picked from commit 984eafba33f7ab288eb82a3b35e9f91b1a7be71a)
HA overview added.

Some review fixes to HA installation guide added.
(cherry picked from commit 4c399293a9c903696e0415c2cc9567ec301cd74f)
Fixing layout of HA documentation.

Making documentation published to verify all the links.
(cherry picked from commit 7d516844fcbaabd489fe52ab5ab2de42d9bf1156)
Fixing page titles and links.
(cherry picked from commit 975bba2ac3d9c61c77b4fa02259c1abd59a8a370)
Fix review comments.
(cherry picked from commit 8eff71401fe80caa88c494761a4018b1195a1dd6)
Yet another part of review fixes.
(cherry picked from commit ec02d316d05e9e5b6e377487fb37be5779058998)
Merge pull request #938 from pasinskim/3.6

3.6 ha documentation