Permit resource paths with underscore in the local resource whitelist.
Merge pull request #155 from edx/jorr/feature/permit-underscore-in-local-resource-path

Permit resource paths with underscore in the local resource whitelist.
Fix an incorrect docstring in the prototype.
Merge pull request #156 from edx/ned/fix-docstring-in-template

Fix an incorrect docstring in the prototype.
Implement Runtime.service and @needs, @wants, and i18n service.

Runtime now has a service() method for returning arbitrary services.
@XBlock.needs and @XBlock.wants let XBlocks declare their requirements.
The "i18n" service provides gettext translations.

Future work involves updating the samples, docs, etc, so that people can
use it well.
Pin pylint so diff-cover works.
Merge pull request #154 from edx/ned/runtime-i18n

Add Runtime.service(), @needs, @wants, "i18n" service.
Close the XBlock mailing list
Merge pull request #157 from edx/ned/close-xblock-mailing-list

Close the XBlock mailing list
Fix the last two pep8 violations.
Merge pull request #159 from edx/ned/last-two-pep8

Fix the last two pep8 violations.
Make Runtime.service work properly in subclasses.

Service declarations weren't propagated down into subclasses.  This made
the whole thing useless, since in the LMS, all XBlocks are subclasses of
their supposed type, since they have had things mixed into them.

This also does a nicer job separating out the fixed XBlock concern (how
do block declare and store their service intentions) and the Runtime
concern (providing the service).

LMS-1562
Tweak pylint
Merge pull request #158 from edx/ned/services-in-subclasses

 Make Runtime.service work properly in subclasses.
Give Runtime implementations more control over how XBlocks classes are loaded from block_types

[LMS-48]
[LMS-181]