* Handle *.go files
* Runs `go build` in the project root
* Needs GOROOT & GOPATH to be set in project env variables
* Display go version in SDK section
* Add project-tree build & rebuild enable support with callback functions

This model is convenient for adding view-more rows to GtkListBox. It can
filter to a fixed number of rows, and then expand them when the expanded
mode is set.

This reverts commit ed3235da.

We need to block startup so that we can persist the doap data back
to the recent-info after open completes.

This alters the implementation of the recent plugin to use the new
IdeGreeterRow.

This base class can be used to create a common form of greeter row between
different sections in the greeter workspace.

We don't need to block anything at startup to discover a doap file. We can
do that in the background as necessary.

This also fixes file-search from the global search as the task completes
allowing the popover to display.

This goes to the same place as close-project, but without closing the
current project.

We might be destroyed while building an index.

Now that the build target is rooted, we can fix the real issue, which is
a file being passed when a string is expected.

Fixes #772