Add info to external graders chapter

Links to example pull/push repositories
Note about graders not accessing student IDs
More fully integrate and test ssl external auth in CMS
Switched from symlink to rename of template
Added missing import of sys to i18n/dummy.py
Removed unused make_dummy.py
Made dummy.py executable
Add "Protein Builder" to "Additional Tools"
Merge pull request #2444 from edx/markhoeber/documentation/LMS-2140

Add info to external graders chapter
Add ProteinBuilder.gif
Merge pull request #2450 from edx/will/fix-dummy-i18n-import

i18n/dummy.py cleanup
Rename of feature AUTH_USE_MIT_CERTIFICATES to AUTH_USE_CERTIFICATES across platform.
Caution! This is backwards incompatible
Merge pull request #2453 from edx/sylvia/documentation/BLD-759

Add "Protein Builder" to "Additional Tools"
Use path.py instead of os.path
Merge pull request #2451 from edx/db/i18n-dummy-path-py

Use path.py instead of os.path
Merge pull request #2032 from carsongee/cg/ssl-studio

More fully integrate and test ssl external auth in CMS
Enable (and test) xml export of pure XBlocks

[LMS-179]
[LMS-209]
[LMS-1345]