[IMP] website_slide: improve the ways to search through courses

PURPOSE

Purpose of this commit is to improve search capabilities of eLearning
frontend application. Searching tags and content should be easier to
do, update and notice.

SPECIFICATIONS

Before this commit
- There is no visual indication to what are the selected filters.
- The user can only select one tag in each dropdown box.
- When the user selects a tag on one course card, this tag replaces all other
filters.
- When the user enters custom search terms, it replaces all other filters.
- When searching a documentation, a stacktrace appears.

After this commit
- Selected tags appear as little tag boxes under the search bar.
- The custom search terms appear as one tag box.
- It's possible to remove a search tag by clicking on the cross present in each
little box.
- It's possible to select multiple tags in each dropdown box.
- Tags in course cards work the same as tags in dropdown boxes, and add
themselves to the list of filters.
- To generate the list of courses to display, a logical OR is operated between
tags of the same group, and a logical AND is operated between groups of tags.
- A logical AND is operated between the custom search terms and other filters.
- A logical AND is operated between the "My courses" options and other filters.
- Bug when searching a documentation is fixed.

LINKS

Task ID: 2080617
PR #39259

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>