issue-293 introduced eslint + husky + lint-staged and fixed major errors

[MartinSunal]

• eslint is used as a linter
• husky is configured as pre-commit hook which will trigger lint-staged in server dir
• lint-staged is configured to run eslint on staged files
• if eslint finds an error then commit is not created until it is not fixed
• all detected eslint errors are fixed except "no-async-promise-executor" which was disabled. At some point all code erroring on "no-async-promise-executor" should be fixed and the rule enabled.
• there is another .eslintrc.json in server/controllers which disables "no-unused-vars" rule because controller's fn signatures were generated so we ignore unused vars.

Fixes #293

[PrathibaJee]

Reviewer is @DanaSunal