Set up linting infrastructure and fix errors and inconsistencies

[effa]

For setup and rules, see https://github.com/adaptive-learning/flocs-visual-components (package.json, webpack config and .eslintrc.json).

The automatic linting is extremely useful for consistent code, and it also teaches how to write good ES6/react code. Currently there are many inconsistencies (mixing different quotes, 2 and 4 spaces, jsx extension for files without JSX, unused imports and variables, etc. - just see what the linter says). (Side note: I would also avoid inconsistent names for different thing, e.g. sthEnv vs. sthEnvironment, pick one and stick with that.)