Better migrate tool installation

[rcaught]

• Doesn't store binary in the git repo
• Updates the jar if a newer version exists (based off file times)
• Manual download instructions

[rcaught]

Don't merge this yet @chrisjones120 (hence the unassign)

[chrisj-devel]

Don't merge this yet @chrisjones120 (hence the unassign)

Too keen

I like where this is going though, let me know when it's ready to go.

[bradleybeddoes]

FWIW GitHub now supports draft mode if you guys hadn't seen it https://github.blog/2019-02-14-introducing-draft-pull-requests/

[chrisj-devel]

FWIW GitHub now supports draft mode if you guys hadn't seen it https://github.blog/2019-02-14-introducing-draft-pull-requests/

That's neat, I didn't know about that