FormFields now allow setting of extra CSSClasses en masse

Each CSS class passed in to `addExtraClass` or `removeExtraClass` will be set as their own key in the `extraClasses` array

Also make `Form` consistent with `FormField`
Adding tests to `FormField` and `Form` for extra classes

Added tests that were missing from `Form` and ones for my new logic
FIX Only and Except rules in Configs not working
FIX changing environment in config.php changes matched yaml rules
Clarify how Only and Except rules combine
Add configuration system tests for Only and Except combinations.
Merge branch 'pr/2173' into 3.1
Merge pull request #2137 from jthomerson/pulls/fix_viewable_data_wrapped_value

FIX: ViewableData wasn't setting values when using default cast
FIX #2174: SearchFilter needs casting helper for DataObject base fields

Commit 964b3f2 fixed an issue where dbObject was returning casting helpers for
fields that were not actually DB objects, but had something in $casting config.

However, because dbObject was no longer calling DataObject->castingHelper, this
exposed a bug that the underlying function db($fieldName) was not returning
field specs for the base fields that are created by SS automatically on all
DataObjects (i.e. Created, LastEdited, etc).

This commit fixes the underlying issue that DataObject->db($fieldName) should
return the field specs for *all* DB fields like its documentation says it will,
including those base fields that are automatically created and do not appear in
$db.
Merge pull request #2175 from jthomerson/fix_2174

FIX #2174: SearchFilter needs casting helper for DataObject base fields
Fixed HTMLEditorField extension call ("updateFieldsForOembed")
FIX HtmlEditorField not re-checking sanitisation server side
BUG Fixed missing allowed_actions on UploadField_SelectHandler
Fixed broken github issue tracker link
Postgres compat in SQLQueryTest
Postgres compat in MemberCsvBulkLoaderTest and GroupTest
PHP 5.5 CI, don't allow failures for sqlite3 and postgres
Merge pull request #2196 from chillu/pulls/travis-matrix

PHP 5.5 CI, don't allow failures for sqlite3 and postgres
Use preg_replace_callback over preg_replace with e modifier
API HTTP::urlRewriter with (string)$code deprecated in 3.1. Fixed regressions and CSS urls.

urlRewriter will expect a callable as a second parameter,
but will work with the current api and simply raise a deprecation error.

HTTP::absoluteURLs now correctly rewrites urls into absolute urls. Resolves introduced in c56a80d6ce

HTTP::absoluteURLs now handles additional cases where urls were not translated.

Test cases for HTTP::absoluteURLs added for both css and attribute links.

Cleaned up replacement expression and improved documentation.