feature #3490 Tweaking Doctrine book chapter (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Tweaking Doctrine book chapter

The doctrine book chapter is a really long chapter, so long I haven't
finished it in my 2 years of sf docs experience ;-). I decided to put
some time in it to make it somewhat smaller.

I planned to do more significant changes, but I think that'll confuse
people. I already think these changes can confuse people, as they might
look for that documentation in the book chapter, while it was moved to
another article or even completely removed. But that might be a first
good testcase for our CHANGELOG plan 😉

But I think it's good to invest time to make our book easy to read
again.

I've worked very precise with commits, in order to easy revert something
and in order to document why I did some changes. If you want some
clarification on some changes, you can read it in the long commit
description.

| Q   | A
| --- | ---
| Doc fix? | yes
| New docs? | no
| Applies to | all
| Fixed tickets | -

Commits
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b4dd1a1 Fixed typo + added remore section
7af962c Rephrased Field Type section
79e2216 Rephrased linking paragraph for Lifecycle events
20ba9e0 Readded small note about parameters
8bb3195 Fixed spelling
91a18cd Changed order to QueryBuilder -> DQL
7acc0d2 Reverted removal of getSingleResult()
c98a3da Adjusted doctrine service tip
f7ec98c Added tip at a more logical place
034d69a Tweaked new cookbook article
18cbacd Clean up reference pointers list
2af5c60 Small tweaks to summary
2c68f04 Moved commands to cookbook
88aa347 Removed types list
c95a68d Removed "Doctrine Extensions" section
13edbcc Removed some duplicated Livecycle docs
22bb029 Minor tweak to configuration section
1ec68fe Minor tweaks to Repository section
485b529 Removed duplicated DQL documentation