comments: notes addition

* A note is a comment on a specific location in the record (e.g., Page 2), main
usecase being paper review before submission;
* Notes are extracted from record comments using regular expressions and a
collection of predefined markers;
* Notes are extracted at comment creation time and persisted in the database;
* Notes are displayed similar to comments, but in a different template (same
base template for both);
* Notes can be hierarchic: Note on Page 1, Fig. 3.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: cosmetic changes

* The comments' text area is now larger;
* Included 'add comment' form tooltip which explains how to add notes;
* Added a warning when viewing the notes, informing the user that this is a
summarized view of the whole record discussion.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: hierarchic notes improvements

* Notes are ordered by creation date (fuzzy);
* Notes are now displayed hierarchically (Note on Page 1, Figure 2);
* Spelling corrections;
* Collapsible notes UI support;
* CSS/ JS in base.html moved to static;
* Disabled collapse href in order to avoid redirections (comments/ notes);
* Refactoring and cleanup.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: notes unit tests and fixes

* Updated note unit tests and fixed some minor found bugs;
* Fixed issue with notes/ comments selected option not being correctly displayed
in UI when no comments existed;

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: notes feature flag addition

* Notes can now be disabled via a configuration flag (disabled by default).

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>