Better checking and meaningfull errors

**Please feel free to comment in this issue and tell what check is missing or what check throw not detailed errors!**

- [x] more info about the need to provide explicit type
- [x] more info about problems with determining GraphQL type for property/argument (@esindger)
- [x] using `@Args` with `@InputType` or without `@ArgsType`
- [x] inform about missing `reflect-metadata` polyfill
- [x] missing `@InterfaceType` on class provided to `{ implements: SomeClass }` (@gdanov)
- [x] more details in message when `GeneratingSchemaError` occured
- [ ] duplicated arg name
- [ ] description/depreciation on not supported field
- [ ] multiple usage of `@Args()`
- [ ] field resolver not matching resolver object type
- [ ] using `@Arg` with `@ArgsType` class
- [ ] duplicated query/mutation name (now it overwrites)
- [ ] overwriting interface/base class field types
- [ ] creating field resolver for method resolver
- [ ] no resolver files match glob pattern
- [ ] detect ES5 compilation (no `Function.name`)
- [ ] detect `undefined` or other invalid values provided by mistake in `type => X`
- [ ] detect wrong `target` setting and arrow function detection issue (#206, #219)
- [ ] more specific error message when root Query is missing (#218)
- [ ] using `defaultValue` option in `@Field` placed in `@ObjectType`
- [ ] abstract type is used directly in GraphQL schema
- [ ] checking implementation of all abstract interface field resolvers
- [ ] inform that decorators don't work on static methods (@karladler)
- [ ] duplicated types/enums before schema auto-check (with stacktrace to point source files)
- [ ] warn about declaring different type (or type options) in `@FieldResolver` than in `@Field()`
- [ ] ...others 😜

Start by choosing one unchecked validation item from the issue checklist and search the repository for its relevant validation or schema-generation entry point. No files or tests are named, so first identify the existing test approach; done means the selected check reports a meaningful error and is verified by the project’s tests.

Written by the indexing model from the issue text.