This removes tables directory_list_{file,dir,rev}, and add corresponding
arrays {dir,file,rev}_entries to the directory table, which was just a
set up to now.

Indexes migrated accordingly.

Intente use is content-by-content lookup (e.g., in the web app), not
mass addition or check for missing contents. We already have
swh_content_missing for that.

query name: swh_content_find_occurrence

given the sha1 of some content, returns info about its origin (type,
url) and context (branch, revision, path)

queries:
- swh_content_find_directory(content_id sha1): content_dir
- swh_revision_find_occurrence(revision_id sha1_git): occurrence

Sample use:

zack-linuxgit-arrays=> select sha1 from content offset 100000 limit 1;
                    sha1
--------------------------------------------
 \xdd63ccef43879c3d7ea47c3f637ef2453f7a58a1
(1 row)

Time: 21,751 ms
zack-linuxgit-arrays=> select * from swh_content_find_directory('\xdd63ccef43879c3d7ea47c3f637ef2453f7a58a1'::sha1);
                 directory                  |            path
--------------------------------------------+----------------------------
 \x24f14db9cc7aa0b106dcb09c9927dfa6712dfd1e | drivers/md/dm-log-writes.c
(1 row)

Time: 729,122 ms
zack-linuxgit-arrays=> select id from revision where directory = '\x24f14db9cc7aa0b106dcb09c9927dfa6712dfd1e'::sha1_git;
                     id
--------------------------------------------
 \x0450b2d120ed9e6d4ac7a6eade0ad116f69b88f7
(1 row)

Time: 395,754 ms
zack-linuxgit-arrays=> select * from swh_revision_find_occurrence('\x0450b2d120ed9e6d4ac7a6eade0ad116f69b88f7'::sha1_git);
 origin |       branch       |                  revision
--------+--------------------+--------------------------------------------
      1 | refs/tags/v4.1-rc3 | \x030bbdbf4c833bc69f502eae58498bc5572db736
(1 row)

Time: 22,006 ms
zack-linuxgit-arrays=>

Only True if found, False otherwise.
And raises ValueError in case of bad inputs (empty input or no sha1,
sha256 keys)

as psycopg2 do not escape for copy_to as it does for other queries

instead of TEXT. Adapt swh_directory_walk_one accordingly