Added the ability to ask for a certain amount of memory in the evaluator.

Note: This is **not** honoured by either the local or the YARN runtimes at this time.
Now transferring the selected memory size into the protobuf sent to the runtime
Added a warning on the YARN runtime if someone uses the API to set the size of the evaluator in megabytes
The local runtime now supports setting the size of the evaluator in MB
The local runtime now supports setting the size of the evaluator in MB
The local runtime now supports setting the size of the evaluator in MB
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into weimer_memore_request
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into weimer_memore_request
Fixed a typo
Merge pull request #673 from Microsoft-CISL/weimer_memory_request

Support for Evaluator requests in MB

I think I'll open a unit test and merge that PR.