PolyScheduler, CosineScheduler and MultiFactorScheduler in Scala feature request.

[satyakrishnagorti]

Noticed PolyScheduler, CosineScheduler and MultiFactorScheduler were missing in Scala. I might contribute if I find some time one of these days.

[mxnet-label-bot]

Hey, this is the MXNet Label Bot.
Thank you for submitting the issue! I will try and suggest some labels so that the appropriate MXNet community members can help resolve it.
Here are my recommended labels: Scala, Feature

[frankfliu]

@mxnet-label-bot add [feature request, Scala]

[piyushghai]

@satyakrishnagorti Welcome to the MXNet community.
We would welcome contributions from you. In case you need any help and assistance, please feel free to reach out to the community on https://the-asf.slack.com (#mxnet-scala channels)