React Forms

[chillu]

This epic implements the RFC as stated in the original issue at #4938. As a part of the acceptance criteria all elements in this RFC should be completed.

• Convert framework forms to bootstrap classes and markup structure (in progress)
• Chosen dropdown
• Treedropdownfield
• Add page. See Add new page layout is broken after form updates in Framework forms silverstripe-cms#1526
• PHP Date/time fields use the wrong template to nest fields. See DatetimeField should use Composite field to render its markup #5672
• PHP The "Visibility" checkboxes within Page settings tab (should use CheckboxSet or similar?) See Visibility checkboxes in Page/Settings use the wrong markup #5679
• Change password fields within security section. See Change password fields within security section are shorter in width #5688
• Go through all legacy code and remove all unused styles

Excludes:

• Buttons
• Tabs