lineForRow changes

On `Editor`, we had 

```coffee
::lineForScreenRow # -> Private; returns a TokenizedLine
::lineForBufferRow # -> returns a String
::lineLengthForBufferRow # -> returns an int
```

Deprecated all those and now we have

```coffee
::tokenizedLineForScreenRow # -> Private; returns a TokenizedLine
::lineTextForBufferRow # -> returns a String
::lineTextForScreenRow # -> returns a String
```

The length can be had via `lineTextFor*Row(row).length`

It also renames several methods in DisplayBuffer and TokenizedBuffer for clarity (eg. TokenizedBuffer had a set of methods named like `lineForScreenRow` even though it took a buffer row as a param). Those entire classes are not public, so there are no deprecations on those methods.

The most interesting stuff is in `editor.coffee` if you want to look / feedback.