added configuration block

I added no semicolon at the end of the PHP echo because in all other examples there exists no semicolon
[#3170] Tabbing out the code example so it's in the sidebar
Merge pull request #3171 from zenobius/patch-1

Fixed typo
Update form_collections.rst

The variable collectionHolder must be assigned inside the jQuery ready function, but must be declared outside, since it is used also in other functions.

I have put back the '$' in front of names of variables having jQuery objects as values and for uniformity, also added it to collectionHolder.
2.3 only - Collection of minor fixes
[Reference][Validation Constraints] Remove invalid default option markers and fix messages
[Reference][Configuration options] Implement consistent headings standard
Change "swiftmailer" and "Swiftmailer" notation to "Swift Mailer"
Revert notation fix of "DependencyInjection component"
Update validator quoting in Yaml files; add value descriptions; fix spaces
Merge pull request #3157 from attardi/patch-1

Update form_collections.rst
Merge branch '2.0' into 2.1
Merge branch '2.1' into 2.2
[#3157] Removing one extra variable change
Merge branch '2.0' into 2.1
Merge branch '2.1' into 2.2
Merge pull request #3168 from bicpi/implement_consistent_headings

[Reference][Configuration options] Implement consistent headings
Merge pull request #3173 from bicpi/fixing_typos_formatting_logic_collection

Collection of fixes: Typos, Formatting, Logic, Links
Merge pull request #3177 from bicpi/fixing_collection_2_3_only

2.3 only - Collection of minor fixes
Merge pull request #3174 from bicpi/another_fixing_typos_formatting_logic_collection

Another collection of fixes: Typos, Formatting, Logic, Links