Removing the feature flags for new header and footer.

Fix acceptance tests

Updating lettuce tests.

Revert the deletion of the original edx header and footer.

Renaming old header and footers to legacy files.

Add IS_EDX_DOMAIN flag for header.

Updating tests and django main template.

renaming the header files for microsite backwards compat.
Merge pull request #5536 from edx/sanchez/remove-new-header-footer-flags

Removing the feature flags for new header and footer.