Replace alchy with sqlservice and unfreeze SQLAlchemy

[northwestwitch]

This PR adds | fixes:

• Fix #251

How to prepare for test:

• Install in a local conda env -> pip install -e . (I've tested it with python=3.8)

How to test:

• chanjo init --auto demodata

• Make sure it has created a directory demodata containing these 3 files:

• Link sample to stats -> chanjo --config demodata/chanjo.yaml link demodata/hgnc.grch37p13.exons.bed

• Load config stats for sample1 ->chanjo --config demodata/chanjo.yaml load chanjo/init/demo-files/sample1.coverage.bed

Expected outcome:

• [x] Get samples mean coverage -> chanjo --config demodata/chanjo.yaml calculate mean -s sample1

Review:

• [x] Code approved by DN
• [x] Tests executed by CR, DN
• [ ] "Merge and deploy" approved by

This version is a:

• [ ] MAJOR - when you make incompatible API changes
• [ ] MINOR - when you add functionality in a backwards compatible manner
• [ ] PATCH - when you make backwards compatible bug fixes or documentation/instructions