Fixed toc and link errors for epub build (Issue #1126). Add cover to epub.

* The epub build is derived from the html build in sphinx; however, some
sections, such as "Welcome" don't make sense to include in the epub.
Essentially, this means that the epub needs it's own toc file which
is what this commit adds (epub-contents.rst). Since there's no
epub_ type option to override the master_doc var, this has to be done
as an arg to sphinx-build.

* This commit also adds a cover to the epub so it looks more like a
real book. The cover isn't great but at least the framework will
be there for someone to add a real cover image.
Don't overwrite LANG in each language's Makefile.

Problem was introduced with last commit. Seems like it doesn't matter
since LANG is passed in with the build command which will override the
Makefile var anyways. Interesting that the en/Makefile is being copied
to all the other languages before build command is issued.
Merge remote-tracking branch 'upstream/master'
Merge pull request #1129 from kmasaryk/master

Updates to epub build
Removed the Facebook Group and Google+ Group

from the "Where to get Help" article as those groups are not intended to be used as help forum.

Many people join those gruops to post requests for help, even though the official group description reads:

"... Please only post topics relevant to CakePHP - This is not a group for support requests - Posts are moderated by group admins - Please keep comments relevant to posts - We do not tolerate spamming or abuse All requests for help should be made through the support channels listed here - http://community.cakephp.org/ IMPORTANT: Joining this group assumes you have read, understood and agreed to these terms."

But as we all know people can't or simply don't do read such messages.
Removing those two from the list should minimize such requests.

Both groups are still listed (rightly) on http://community.cakephp.org/ and under the community menu on http://cakephp.org/.
Updates Plugin Configuration 

Updates the plugin configuration section with information on the `ignoreMissing` option.
Spelling error in plugins.rst

Corrected boostrap to bootstrap
Add some details around form tampering.

Refs cakephp/cakephp#1967
Merge pull request #1139 from jtyost2/patch-1

Updates Plugin Configuration with ignoreMissing option
Fix formatting.

Refs cakephp/docs#1139
Improved 'Hashing passwords' example.

The previous example checked if an id was set in the model, and therefore may save passwords in plaintext if an id was set and a password field was submitted with form data. My change simply checks if there's a password field from the form data and hashes it.
Merge pull request #1142 from ojtibi/patch-1

Improved 'Hashing passwords' example.
[fr] Follow 8cb6e0b042e62c27038495c8bcdf53cf1220d8ec

Removed the Facebook Group and Google+ Group
[fr] Follow #1139

Updates Plugin Configuration with ignoreMissing option
[fr] Follow 41be3499747de7d7933a84550af307e624411210

Add some details around form tampering.
[fr] Follow #1142 & more

Improved 'Hashing passwords' example.
Missplaced 'and' moved.
Merge pull request #1153 from sam-at-github/routing-connectNamed-correction

Missplaced 'and' moved.
All TOC's should be limited in depth.

Giant duplicated TOCs can be really confusing to some readers. Lets not
do that.

Refs #1149