Summary:
We used to call the database twice for directory listings. We now
special-case the empty directory, which allows us to only call the database
once, saving one round trip on the most used query.

Test Plan: Unit tests updated

Reviewers: anlambert, #reviewers!

Differential Revision: https://forge.softwareheritage.org/D337

This commits adds a popover panel reachable from the 'Show identifiers'
entry in the 'Actions' menu for displaying swh persistent identifiers
related to the currently browsed objects (content/directory/release/
revision + snapshot context if any).

The panel offers easy copy to clipboard of the swh ids and related
urls but also the possibility to add optional parts (origin info
for instance).

Closes T1004

Closes T1050

When clicking on the 'Browse' menu entry, redirect to the search page
if no swh objects were previously browsed in the current browser
session instead of displaying an info text.

This commits adds support for optional parts of persistent identifiers
in swh-web in order to add origin context when resolving the swh object
to browse. It is also possible to set lines to highlight for swh content
object.

Also to be noted, persistent id urls are now rooted to / instead of
/browse. Nevertheless backward compatibility is maintained for HAL.

Closes T1042

This commit improves the overall design of swh web applications by
making it more compact in order to gain more space for displaying the
archive content.

The following changes have been applied:

  - use a collapsible sidebar for switching between the different
    features (currently Web API, Browse, Search, Vault, Help) instead
    of putting them in the top navbar

  - remove the use of panels (cards in Boostrap 4.x) as the main layout
    for swh-web pages, instead move their headers in the top navbar and
    use their content as the main page layout

Closes T1052
Closes T1032

Closes T1067

Closes T1065

When one wants to display a content, HTTP requests are sent to the indexer
storage in order to retrieve the associated mime type, language and license.
Those requests may fail so properly handle errors in order to avoid
content display errors.

Closes T1060

This commit removes the collapsible panel, located in the top
part of numerous views, used to display the metadata associated
to a swh object in favor of a popover reachable from the Actions
menu located on the right of the view.

Related T1052

When a README is written in reStructuredText (rst), convert it to html server
side through the use of pypandoc in order to get a proper display of it.

Indeed, the client side library used to render markdown (showdown.js) does
not handle rst properly and there is no viable solution to convert rst
to html directly in the browser.

Related T1061

  - prefer to display a smaller spinner in the left of the search panel
    header instead of a big one at the center of the screen

  - clean the search results table when performing a new search

Closes T1056

This commit adds query parameters to some context indedependent views
in order to add origin info.

Closes T1055

Closes T1054