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 popover 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;
* Replies to original comments can be sent directly from the notes page;
* Radio buttons to switch between comments and notes;
* Notes feature flag.

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>
unit tests

* 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;
* utils.washers unit tests

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

* Available at /record/XX/comments_pdf, for records with PDF attached;
* Requires CFG_PATH_PDFTK and CFG_PATH_IMAGE_MAGICK_CONVERT.

Signed-off-by: Adrian-Tudor Panescu <adrian.tudor.panescu@cern.ch>
comments: PDF preview first/ last page buttons

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