Serial Control: Embed Alternate Interfaces
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As another step toward a unified interface, the serial control subscription
editor now consists of an embedded version of the alternate control. This
reduces duplication of both code and documentation, and smoothes the eventual
transition to a single interface.

In order to not lose any essential features, the following additions were made
to the new combination editor:

* note editors on subscriptions and distributions
* labeled dropdown for distribution summary options ("Add to record entry", "Use record entry only", etc.)
* legacy record entry linkage setup (Allows one to tie a distribution's information to a particular serial record entry (i.e. a MFHD record))