Support SQLite as a database

[taraio]

Is your feature request related to a problem? Please describe.
Add support for sqlite using ecto_sqlite3 https://github.com/elixir-sqlite/ecto_sqlite3

[Clivern]

Actually i wanted to support SQLite for small setups and testings but sadly it doesn't support SELECT ... FOR UPDATE OF. Currently i use that for locking support, to lock an environment from a concurrent updates.

Reference https://www2.sqlite.org/cvstrac/wiki?p=UnsupportedSql

SELECT ... FOR UPDATE OF ... is not supported. This is understandable considering the mechanics of SQLite
 in that row locking is redundant as the entire database is locked when updating any bit of it. 
However, it would be good if a future version of SQLite supports it for SQL interchageability reasons if nothing else. 
The only functionality required is to ensure a "RESERVED" lock is placed on the database if not already there.

[taraio]

Maybe we can switch to ecto locks https://hexdocs.pm/ecto/Ecto.Changeset.html#optimistic_lock/3. Not sure if it fits as replacement or not. it does fetch a version and update with that version so other update requests will fail if they try to update since they use stale version.

[Clivern]

We can use https://github.com/whitfin/sleeplocks to replace the db based locks. I will test this in a different project and if it works as expected, i will add it to lynx.