Mixin support

[canonic-epicure]

This PR adds support for mixins, as per https://www.bryntum.com/blog/the-mixin-pattern-in-typescript-all-you-need-to-know/

The most important changes:

• When doing "inheritance" in class and interface converters, consider the possibility for the base type to be intersection type: Type1 & Type2. In such case, "inherit" from every component of such type
• When doing reflections merge, do not merge the reflections for type with reflections for values. This is because TypeScript has different namespaces for values and types and its perfectly valid to have different things with the same name:

export type Some = number
export const Some = () => {}

• bumped TypeScript dependency to 3.3.x

[aciccarello]

Awesome! I wonder if this will help with any other reflection mergin issues we have.

[aciccarello]

So the build passed on Node 10 but not node 6 because of a tslint error. That seems strange...

ERROR: /home/travis/build/TypeStrong/typedoc/src/lib/converter/components.ts:9:9 - missing whitespace
ERROR: /home/travis/build/TypeStrong/typedoc/src/lib/converter/components.ts:9:18 - missing whitespace
ERROR: /home/travis/build/TypeStrong/typedoc/src/lib/output/components.ts:8:9 - missing whitespace
ERROR: /home/travis/build/TypeStrong/typedoc/src/lib/output/components.ts:8:18 - missing whitespace

Sorry it's so grouchy. 👿

[canonic-epicure]

I was not changing those files, but added whitespace anyway, hopefully build will pass this time :)

[aciccarello]

Nice work! This looks great. Only remaining issue is that I would like to have render tests though so we make sure this doesn't break in the future. The example is helpful but won't alert us if things change.

[aciccarello]

Great Work!

[canonic-epicure]

@aciccarello Thank you!