Add sysadmin dashboard

[carsongee]

For seeing overview of system status, for deleting and loading
courses, for seeing log of git imports of courseware. Includes command
for importing course XML from git repositories.

This is the cleaned up branch from #654 with a single commit.

[singingwolfboy]

Nitpick: this seems like it would be nicer as:

new_dir = "{course_dir}_deleted_{timestamp}".format(course_dir=cdir, timestamp=int(time.time()))

[cpennington]

It would be good to take a look at https://jenkins.testeng.edx.org/job/edx-platform-report/1277/Diff_Coverage_Report/? (the diff-coverage report for the build) and see if you can cover some of the missing lines. It looks like it's mostly error cases that aren't being tested.

[sarina]

@carsongee does this supercede #654 ? if so can you close the old PR?

[carsongee]

I went ahead and closed 654. I'll take a closer look at coverage and see if there are some easy ways to get more coverage, but I am bit starved for time at the moment so it may not be until Monday.

[carsongee]

I've added a lot of tests, and fixed some code as a result. This is about as good as I can get without a lot more work for not much gain.

[cpennington]

👍

[singingwolfboy]

👍

[carsongee]

Thanks for the extensive reviews, and accepting the code.