GH components

[gonzalocasas]

This is still a draft pull request, it adds a first batch of GH components but perhaps more importantly, sets up the project to add more in the coming days.

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I added a line to the CHANGELOG.rst file in the Unreleased section under the most fitting heading (e.g. Added, Changed, Removed).
• I ran all tests on my computer and it's all green (i.e. invoke test).
• I ran lint on my computer and there are no errors (i.e. invoke lint).
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[beverlylytle]

I know this is still a draft, but I made some comments on the docs anyway... ;)

[beverlylytle]

not float?

[gonzalocasas]

not float... ABB RAPID is an inflexible friend sometimes... :P

[beverlylytle]

but

if not speed or speed < 0.01:
            add_warning('Speed must be greater or equal to 0.01 mm/s.')

[beverlylytle]

missed a couple...