mediawiki: simplify apache config

- use includes wherever possible
- add a "public rewrites include"
- add the configurable apple touch icon using this include.
- make the math redirect now respects RW_PROTO if present
- added retry=0 to all the proxypass directives

This change supersedes Ieb55283f7b33c589bec71e9e17f170948a57d3b8 and
I515deb3ae5e8a30435360fcace587ac298d0e73a .

Change-Id: I440f2e37a437c96af4c7be7d1ca5255a16eecaa0
Signed-off-by: Giuseppe Lavagetto <glavagetto@wikimedia.org>