IE10+ TinyMCE Links compatibility

The patch makes linking stuff in the RCE possible on IE10+. The reason
it was not functioning on IE9+ is because the "fix" for IE is installed
only if the browser is identified to be IE, while our detection code was
not able to detect versions past 9.

Closes CNVS-5644

TEST PLAN
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When I say the link "works" in the steps below, it means 4 things:

  1. the word text is not modified
  2. the word becomes highlighted in blue and underlined as a link
  3. the word stays in its place
  4. the word actually becomes a clickable link (viewable only when
     you're viewing the content as opposed to editing it)

  - create a discussion
  - using Chrome/FF: type some words, then select a word in the middle
    and link it to any web page:
    - verify that the link "works"
  - save the discussion
  - now using IE8, IE9, IE10, and IE11:
    - edit that discussion
    - add another sentence, and link a word in the middle:
      - verify that the link "works"
  - don't hate me

> Optional: embedding YouTube videos

  - enable the YouTube LTI
  - embed a YT vid in the discussion content
  - verify that when you're adding or modifying links using IE, the
    video doesn't disappear or gets broken (as was reported by Caleb)

CR NOTES
-- -----

  - the test for IE10 is done using the conditional JS compiling, which
    is dropped in IE11+
  - the test for IE11 is done by sniffing the UA for Trident and rv:
    11.0
  - in order not to introduce any side-effects, I kept from installing
    an "ie" class on the root document elements in the case of IE10+

Change-Id: I61d6ac1918291eb8df6da1aa270ef8358ed49a8f
Reviewed-on: https://gerrit.instructure.com/29651
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>