Replace ace-editor

[StianJul]

Replace the ace-editor with a new editor based on standard usage a textarea with markdown support. For example, the GitHub issue-editor seem to solve this pretty well.

Due to multiple issues that have come up, both in Devilry and the ace-editor GitHub-repo (ajaxorg/ace#2164), regarding accessibility issues and improvements, this seems to be way forward instead of trying to make the ace-editor accessibility-friendly.

Features to look into with a new text-editor:

• Auto-growing textarea
• "Flip" editor to a confirm-box before submitting.
• Handle notifying users about existing "editor content", such as written text and uploaded files, if they try to navigate a way.
• Better support for LaTeX and code snippets.

[torgeirl]

@StianJul: In addition to the above mentioned, better support for LaTeX and code snippets are highly requested features.

[StianJul]

We did not have time to implement better support for LaTeX and code snippets. #1220 has been created for this and added to milestone 5.5

[StianJul]

This update must be seen together with the WCAG-improvements to file-uploader. The fileupload-improvements disables posting until the files are uploaded.

This is the closest we can come to preventing the user from submitting a "delivery" without adding extra steps for submitting.