[SVN] Key bindings for various toggle functions

[Allan Odgaard]

Currently we have:

  Toggle "String" / :Symbol              ⌃⇧S
  Toggle CamelCase / underscore_words    ⌃⇧S
  Toggle String Quotes (Single / Double)   ⌃"

I suggest we change it to:

  Toggle "String" / :Symbol                ⌃:
  Toggle CamelCase / underscore_words      ⌃_
  Toggle String Quotes (Single / Double)   ⌃"

I think these keys are better -- having just one key to toggle  
current entity would be nice, but since these overlap in scope, that  
is not possible.

Note btw that on the US keymap all the keys actually use ⌃⇧ as  
modifiers, which is the “bundle item namespace”.

Any thoughts/objections (I realize that it makes them slightly harder  
to reach, not sure how big a deal that is -- given that they are  
rarely used, having a good mnemonic would likely be more important  
than easy to reach)?