Attach changelog message to modified-module feature

[tgqiang]

Taken out from #26

This issue is raised as per the professor's comments on Modified Modules feature. (Given use case: "User can specify a message explaining/detailing reasons for the change applied to a module")

@helloqx @nlzz22 @xaterz @a0129998
Requires addition of change-log message attribute in back-end, and this will affect Edit Module and Modified Modules features.

This issue is not a high priority currently.

[tgqiang]

Due to time constraints, we will not be implementing this feature. This issue will be left open, however.