comments: rework/rewrite javascript for inline comment handling

There shouldn't be any functional changes here, but the focus has been on doing
the right thing instead of looking at how it was before.

Incremental cleanup did not seem feasible. I think this is more readable and
maintainable than before ... at least for me.

Existing snippets has been reused when reimplementing. The new implementation
focus on being as simple as possible and well-structured. jQuery and data
attributes are used instead of custom implementations. Some existing functions
have been modified or renamed, others have been removed when they no longer
were needed.