Integrate BuildStream into an IDE

[See original issue on GitLab](https://gitlab.com/BuildStream/buildstream/-/issues/972)
In GitLab by [[Gitlab user @adds68]](https://gitlab.com/adds68) on Mar 25, 2019, 14:59

## Background

Many developers require IDE to develop.

## Task description

* [ ] Build a plugin for GNOME Builder: https://gitlab.gnome.org/GNOME/gnome-builder/merge_requests/179

## Acceptance Criteria

You can use BuildStream from inside GNOME Builder

----
[//]: # (To review information about possible relevant labels for this issue please view the list of labels: https://gitlab.com/BuildStream/buildstream/labels)

Start by reading the original GitLab issue and the linked GNOME Builder merge request 179 to understand the proposed integration. Identify the plugin scope and how BuildStream should be invoked from GNOME Builder; done means BuildStream can be used inside GNOME Builder as described by the acceptance criterion.

Written by the indexing model from the issue text.