Fix bad interaction between pluggable InputTypes and Microsites

Pluggable InputTypes use edxmako.paths.add_lookup to inject new
mako template directories. Those were getting clobbered by microsites
(and by theming), which were completely rebuilding the mako template
lookup list from scratch.

This commit switches those two features to use the same add_lookup
function as pluggable InputTypes.

[LMS-2489]
Revert "Open ended panel headings not internationalized."

This reverts commit eb9133aeb687c0d103feec16371ad7d2bce952a8.

ORA-352
Merge pull request #3168 from cpennington/fix-lms-2489

Fix bad interaction between pluggable InputTypes and Microsites
Merge pull request #3176 from edx/hotfix/revert-openended-i18n

Revert "Open ended panel headings not internationalized."
Updating the hash of the ORA2 release candidate in the requirements
Merge pull request #3186 from edx/sanchez/update_ora2_hash

Updating the hash of the ORA2 release candidate in the requirements
Merge remote-tracking branch 'origin/release'