backend: Add db support and minimum project level settings

[mariusmucenicu]

• Added SQLAlchemy SQL Toolkit (set of tools for working with databases and Python)
• Added SQLITE3 db as the main db for this project
• Added default project settings and a way to override them with production/development settings when necessary.

Resolves #153

[codecov[bot]]

Codecov Report

Merging #154 into master will decrease coverage by 0.88%. The diff coverage is 73.07%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
- Coverage   99.47%   98.58%   -0.89%     
==========================================
  Files           7        9       +2     
  Lines         757      780      +23     
==========================================
+ Hits          753      769      +16     
- Misses          4       11       +7

Impacted Files	Coverage Δ
core.py	100% <100%> (ø)	:arrow_up:
knowlift/default_settings.py	100% <100%> (ø)
knowlift/db.py	56.25% <56.25%> (ø)

---

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 c697ad8...fb96eeb. Read the comment docs.