fixes https://github.com/TryGhost/Toolbox/issues/150
- up until now, the test framework has copied all theme fixtures to the
test directory when it boots Ghost
- the vast majority of tests don't need all the themes, so this is quite
a wasteful operation
- this commit disables copying all themes by default, and provides the
`copyThemes` boot option to enable this
- also adds a `copySettings` option, and defaults `redirectsFile` to
false to further reduce the number of file copies
refs https://github.com/TryGhost/Toolbox/issues/354
- this commit turns the Ghost repo into a monorepo so we can bring our
internal packages back in, which makes life easier when working on
Ghost
