Replace the ASCII art arrows (<->) with real arrow symbols (⇄).

This replaces the former ASCII art arrows with real unicode arrows.

**Admin:**

![ascii-art-arrows](https://f.cloud.github.com/assets/48491/1432504/ac0470d4-40df-11e3-8d19-5303a2f725f7.png)

![real-arrows](https://f.cloud.github.com/assets/48491/1432531/32470a12-40e0-11e3-9839-8db420fc2ec7.png)

**SysConfig:**

![ascii-art-arrow-sysconfig](https://f.cloud.github.com/assets/48491/1432929/695465f2-40e7-11e3-94a5-3ed9dd1de70c.png)

![real-arrow-sysconfig](https://f.cloud.github.com/assets/48491/1432930/695d1c56-40e7-11e3-94fb-d464f5cb3c8c.png)

Now that all OTRS supported browsers made it into the 21st century, I finally feel like it's time to do this replacement.
Tested on:

  * Linux
    * Firefox 24.0
    * Chromium 30.0.1599.101
  * Windows 7
    * Firefox 24.0
    * IE 10.0.9200.16721
    * Opera 17.0.1241.53