Updated .gitignore to ignore Sphinx files
Bootstrapped Form component chapter
Introduction chapter for the Form component
[WIP][#1883] Adding more and more details for the form introduction

Still a WIP because:

a) Bernhard will certainly need to review it
b) I would like to re-read it - I felt that there are still gaps - too many details here, too few details there
c) This is part of a larger, on-going project to refactor the forms docs
d) We need to bootstrap the validation and translation component docs, and other things need to be refactored to make sense
[Form] Making updates per @bschussek and fixing some markup issues
Removing .gitignore file - putting the sphinx build files right in this directory is just one option
[Form] Removing constants, just to avoid confusion about them being somehow important internally
Merge pull request #1883 from bschussek/form-intro

[Waiting Code Merge] Introduction chapter for the Form component
add missing word
Added missing tilda (yml config)

The tilda was missing for the YAML configuration.
Merge branch '2.0' into 2.1
Fixed build
remove obsolete note on monolog.logger tag
added a missing security advisory
Merge branch '2.0' into 2.1
Merge pull request #2987 from greg0ire/missing_word

add missing word
Merge branch '2.0' into 2.1
Merge pull request #2991 from WouterJ/build_error

[2.1] Fixed Build errors
Merge pull request #3006 from havvg/2.1

remove obsolete note on monolog.logger tag