Track client cursor position internally

[NuSkooler]

Issue:
Currently the system relies on ANSI DSR (Device Status Report)/CPR sequences in many areas to discover / track client cursor positions. Not limited to:

• MCI position
• Pause
• Some work in the FSE

This has some major drawbacks:

• Does not work in all terminals. Some terminals such as mTCP's telnet only partially work as their queue of DSR's is very small. Many older DOS terminals do not implement it at all.
• Introduces a lag (essentially, we must SYN/ACK the positions).
• May be wrong by the time we get the data, i.e.: if data scrolls (See MCI codes break for art with a height greater than term height #5)

Since we know the term dimensions, we should track the positions ourselves. This has some implications around the current implementation of Views, ansi_term.js's goto(), etc.

Also related: Some code saves/restores (SCP – Save Cursor Position / RCP – Restore Cursor Position) which may need to go as well.

[cognitivegears]

See my potential solution in PR #407. I'm not 100% that this won't cause any regressions yet, but if you agree I'd love to get it in and would be happy to help work through any that might (will probably) come up.

[NuSkooler]

Big shout to @cognitivegears for the work on this!