Fix/repeating aliases in nested relations

[VLZH]

To fix this issue: #55.

[VLZH]

I had thought long time about adding a new property to JoinOption like alias. To use something like this:

@Crud({
  // ...
  query: {
    join: {
      category: {},
      'category.image': {},
      tags: {},
      'tags.image': {
        alias: 'image2'
      }
    }
  }
})
class MyController {
  // ...
}

What do you think about this?
My realization without a new option.

[VLZH]

I will add commit to fix coverage test in 1 day.

[VLZH]

In this method, I do not understand why the filters were added before joins? Is there a reason for this? My reason to change ordering is that some filters would do not valid until relation do not add to entityRelationsHash.

[michaelyali]

great work, @VLZH !
I'll fix some conflicts because I've merged my PR recently and will merge this.
Thanks a lot!

[michaelyali]

Closing this in favor #287