Build process always builds all tabs

[Cloud7050]

Steps to reproduce:

1. Run yarn build and wait for it to successfully complete
2. Run yarn build again
3. The script will save on processing where it can for the JSONs and bundles (unsure about the HTMLs), but the tabs that are listed and get built seem to always include everything

From past discussions and testing, I was under the impression that the previous build system's method of saving on processing would carry over. Ie, without the force flag, tabs would only be built if any of their files had been updated since the last build (or if they were never built before), or if their relevant bundle got updated (because a tab may import data from its bundle, where the bundle's files got updated without the tab's files also needing updates). Therefore I do not think this behaviour is intentional.

[Cloud7050]

Obsolete via merging #163