Add ace-modes to javascript manifest, fixes #7513

##### What does this MR do?

This PR adds most of the modes of ace editor to the javascript manifest. With this PR, there is syntax highlighting while editing a file. I've included all modes which file size is less than 120k.

Additionally it adds syntax highlighting, when creating a new snippet or file via web interface. The mode is determined on the current entered filename and tracks if the user changes it.

##### Why was this MR needed?

Currently, when opening a file (e.g. a markdown), ace editor tries to load the mode file. Since it's not in the manifest, a 404 error is raised behind the scenes, and no syntax highlighting is available.

##### What are the relevant issue numbers / Feature requests?

This PR fixes
*  #7513
* #6850
* http://feedback.gitlab.com/forums/176466-general/suggestions/6300274-syntax-highlighting-in-editor-while-editing-and-cr

/cc @cirosantilli 

##### Screenshots (If appropiate)

![screenshot 2014-08-18 12 24 15](https://cloud.githubusercontent.com/assets/278301/3950277/1abf0628-26c3-11e4-8de1-69dc7f919236.png)

![screenshot 2014-08-18 12 26 02](https://cloud.githubusercontent.com/assets/278301/3950283/23d50cd0-26c3-11e4-9bd1-7d2c18a86d24.png)

![create_file](https://cloud.githubusercontent.com/assets/278301/3951324/45f9dd8e-26d4-11e4-8cc9-4e82ea4a7b91.gif)


Is it not possible to factor this out with the analogous block on `new_tree/show.html.haml` ? Seems the same except for one class name.