Write better code

[wgrabowski]

Due to some interest of this tool I've took a look in my code and I think it can be written in better way.

Rewrite code to be faster and more focused:

• remove ts-morph dependency, rely only on Typescript APIs
• don't count all usages of given class, check if it has any relevant usage (if even one usage is found then return true, process less files, should be faster)
• tool should do what it's name says, nothing more - found Angular classes that have no relevant usages in other files, therefore it should return only list of class names with their source files
• when looking usages by selector only look in relevant files (currently is filtering all files)

Improve cli:

• use some library for cli interface (probably cac)
• add flag for spec file pattern (default *.spec.ts)
• add --ci flag to skip progress in output (or flags for human readable and machine readable output)
• • consider adding flags for --components, --pipes, --directives, --injectables

Fix errors reported by community

[wgrabowski]

also avoid creating too many generic functions that are used only for one thing

[wgrabowski]

also get source files from angular.json as relying on tsconfig works only if files are spcecified in it