Removed duplicated DQL documentation

The doctrine docs already has a big great documentation on this. There is
no reason to duplicate it in the sf docs. This commit removes everything
except a simple example.

It also moves the sentence about the return result above, since that makes
more sense now the getSingleResult example is removed.
Minor tweaks to Repository section
Minor tweak to configuration section
Removed some duplicated Livecycle docs

The list is also included in the doctrine docs. There is no need to
duplicate that in the sf docs. And if it's usefull, it certainly isn't
when there is no more documentation about their meaning.
Removed "Doctrine Extensions" section

It's enough to add it to the "Read more" list, there is no need to
introduce each cookbook article in a seperate section.
Removed types list

This is really doctrine specific, the sf docs should not document this,
kind of SoC for docs :wink:.
Moved commands to cookbook

It's not really basic information. All important commands are already
discussed in the rest of the chapter. The rest are just usefull commands,
which is a perfect topic for a cookbook.
Small tweaks to summary
Clean up reference pointers list
Tweaked new cookbook article
Added tip at a more logical place
Adjusted doctrine service tip
Reverted removal of getSingleResult()

It's now smaller (25 to 3 lines) and uses getOneOrNullResult().
Changed order to QueryBuilder -> DQL

The QueryBuilder seems to be easier and more recommend to use. This meant
the QueryBuilder section now contains the primary information and the DQL
section is now reduced to somewhat a "side topic".
Fixed spelling
Readded small note about parameters
Rephrased linking paragraph for Lifecycle events
Rephrased Field Type section
Fixed typo + added remore section
Update checkbox_compound.rst.inc