Fix installer issue step 4

https://github.com/pyrocms/pyrocms/issues/3247?codekitCB=417737337.007735#issuecomment-38970490
Simplified the EntryModelGenerator
Polymorphic Keywords
Polymorphic keywords migration
Fix some errors in pages module
Fix some pages bugs for page types

Keywords still is broken here - updated methods no doubt
File type should be relationship
Cleaner file names
Temp keywords workaround
Merge branch 'refs/heads/2.3/develop' into 3.0/develop

Conflicts:
	system/cms/modules/blog/details.php
	system/cms/modules/navigation/views/admin/index.php
	system/cms/modules/pages/controllers/admin_types.php
	system/cms/modules/streams_core/field_types/file/src/Pyro/FieldType/File.php
	system/cms/modules/streams_core/field_types/keywords/src/Pyro/FieldType/Keywords.php