[WIP] Init Command

replaces https://github.com/cordoval/manager-tools/pull/16

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #
| License       | MIT
| Doc PR        | not yet

What it does?

* Validates if exists a valid `.manager-tools.yml` file, if not asks you to run the  `configure command`
* The configure command does the following:
   * If not exists, creates the `MANAGER_TOOLS_HOME` folder under the user `HOME` folder
   * Asks your credentials for github
   * Asks if you want a different `cache-dir` instead of the default **"cache"** folder placed under the `MANAGER_TOOLS_HOME` folder
   * Saves the data into the file `.manager-tools.yml` inside the `MANAGER_TOOLS_HOME` folder
* You can always **override** the `MANAGER_TOOLS_HOME` and `MANAGER_TOOLS_CACHE_DIR` by setting those as an environment variables (`ENV`)