Build hashes

[huwshimi]

Done

• Add hashes to the built file names to help with updating caches.
• Load css files in the single-spa template to improve app loading.

QA

• Run dotrun, the app should load normally for the react/angular apps.
• In a local MAAS run the following:

git config --file=.gitmodules submodule.src/maasui/src.url https://github.com/huwshimi/maas-ui.git
git config --file=.gitmodules submodule.src/maasui/src.branch build-hashes
git submodule sync
git submodule update --init --recursive --remote
make clean-ui
make ui

You may have to use SKIP_PREFLIGHT_CHECK=true make ui like I did.

• The app should load normally for the react/angular apps.
• There should also be a small improvement to the content flash when switching between apps.

[squidsoup]

Looks good. The transitions feel less jarring now, thanks @huwshimi.