Merge branch 'master' of https://github.com/NobrainerWeb/Silverstripe-Section-Module

First go at many_many objects - sorting not working
Scope public vars to private
Attempt to get sorting working on may_many

Still no luck using grid field extensions for sorting many_many.
Using sortablegridfield to have many_many sortable sections
Option to relate/remove a section to/from pages

Also showing a warning message when a section is in use on more pages
than one (Global).
Set searchable fields for related pages
Add requirement for SortableGridfield module
Update to requirements and read me
Merge branch 'Many_many'
Merge branch 'master' of https://github.com/NobrainerWeb/Silverstripe-Section-Module
Merge branch 'Many-many'