Database set-up

[gdetrez]

This is a partial implementation of a persistence layer using PostgreSQL. The idea is to discuss the approach before I set-up all the tables and change the corresponding code. What's included:

• install dependencies (sqlalchemy, psycopg...)
• set-up package structure: I created a new package instead of using scanomatic.io to group the database related modules together.
• setup flask to connect to the database
• add postgres to docker-compose
• set-up a migration framework
• update the docker image to execute migrations when starting
• add a table for the scanners
• add a gateway class to save/fetch scanners from the database

Some notes:

• Running the migration in the docker entrypoint makes things simple right now but it may not be the most efficient thing. And the container will not start if the database is not reachable.
• I choose to not use the sqlalchemy ORM. This works well with the current models and will hopefully be more flexible when we will want to store arrays in the database.
• on the python side my idea is to split ScanningStore, loosely following the different APIs (scanner, scan, scanjob...)

[codecov-io]

Codecov Report

Merging #299 into master will increase coverage by 0.28%. The diff coverage is 91.52%.

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
+ Coverage   37.39%   37.67%   +0.28%     
==========================================
  Files         159      165       +6     
  Lines       16215    16311      +96     
  Branches     2902     2905       +3     
==========================================
+ Hits         6063     6145      +82     
- Misses       9732     9744      +12     
- Partials      420      422       +2

Impacted Files	Coverage Δ
scanomatic/ui_server/scanners_api.py	98.52% <100%> (+0.19%)	:arrow_up:
scanomatic/data/tables.py	100% <100%> (ø)
scanomatic/io/scanning_store.py	95.77% <100%> (-1.6%)	:arrow_down:
scanomatic/ui_server/scan_jobs_api.py	92.59% <100%> (+0.28%)	:arrow_up:
scanomatic/ui_server/database.py	100% <100%> (ø)
scanomatic/scanning/update_scanner_status.py	95% <100%> (-5%)	:arrow_down:
scanomatic/data/scannerstore.py	100% <100%> (ø)
scanomatic/ui_server/ui_server.py	35.53% <50%> (+0.49%)	:arrow_up:
scanomatic/data/migrations/env.py	71.42% <71.42%> (ø)
scanomatic/data/util.py	75% <75%> (ø)
... and 10 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 0d7601e...5010739. Read the comment docs.

[coveralls]

Coverage increased (+0.2%) to 43.006% when pulling 5010739fd48b214c199994e06bf07f5599959d76 on gdetrez:database into 0d7601e08b1876358aed8addc70bb500c5cc7792 on Scan-o-Matic:master.

[gdetrez]

@local-minimum @dindinoh : I made a slight change to the way the database is configured: using multiple environment variable (PGHOST, PGUSER...) instead of one and allowing us to store the database password in /etc/scanomatic/pgpass.