Add alias categories

## Expected Behavior

Aliases should be decorated with `CakeAliasCategory` alias, see [guidelines](https://cakebuild.net/community/contributing/documentation#methods)

## Current Behavior

`CakeAliasCategory` is not set.

## Possible Solution

Set `CakeAliasCategory` on aliases.

## Steps to Reproduce (for bugs)

1. Go to https://cakebuild.net/extensions/cake-teamcitycoveragereporter/ --> No aliases listed
2. Go to https://cakebuild.net/dsl/ --> Aliases from this addin are not listed
3.
4.

## Context

Using `CakeAliasCategory` improves documentation of alias on website.

## Your Environment

* Addin version used: 0.2.2
* Cake Version used: N/A
* Operating System: N/A