Add inline commit coments

[coder1125]

Adds inline comments to commits. Inline commit comments can be considered new feature and does not use the existing
functionality of comments, issues or attachments.

/claim #4898

[wxiaoguang]

A quick look, still many problems:

• Some functions have security problems (for example: DeleteCommitAttachment can delete any attachment by UUID)
• Some designs are strange (for example: there is no ctx.Session.Get("attachmentsMaps") in existing code base, it looks not right)
• Too many if-else logic (in go and tmpl code) for "different pages", it is quite fragile
• Incorrect tmpl variables (for example: ctx: ctx.Data can't be right)
• Incorrect logic (for example: CancelCommitComment)
• Many functions have complex logic, so they need tests.

So overall it doesn't look good enough. If it can continue, please review the changed code line by line and add necessary tests. (by the way: I only take a quick look for the code, I haven't really thought about whether the design is feasible).

[coder1125]

From the list, the following are resolved

• Incorrect tmpl variables (for example: ctx: ctx.Data can't be right) The line was added for testing and has been removed.
• Incorrect logic (for example: CancelCommitComment) Corrected logic by throwing ServerError if error exists.
• Rename CommitData to CommitComment
• Added ReplyToCommentID column. When replying to message, the commentid of the original message is stored in ReplyToCommentID.

[lunny]

What's the design how to cooperate with attachment table? The attachment maybe GC because all foreign indexes are zero?

[coder1125]

The design is based on the proposed solution, the commitcomment table is not dependent on attachment table. Further details about handling of foreign indexes need to be provided and/or discussed.