New feature: get Project Components

[edegaudenzi]

Functionality to retrieve Components defined in a Jira project is missing.

Something like:

$proj = new ProjectService();
$prjs = $proj->getAllProjects();
// Extract and show Project Components for every Jira Project
foreach ($prjs as $p) {
    var_export($proj->getProjectComponents($p->id));
}

I'll try to create a pull request about this.

[lesstif]

Hi @edegaudenzi, I'm looking forward to your PR.

[edegaudenzi]

Hi @lesstif , you're more than welcome. I think PR's up.

[lesstif]

Hi @edegaudenzi , Thank you for your great PR.
Could you update README.md with sample code, please?

[edegaudenzi]

It should already be in the first commit. I've tried to follow existing code style and naming convention but will definitely need your review! ;)