Use property/env variable to specify frontend version

[inodb]

Currently we can only change frontend version by changing portal/pom.xml. We should change this to an environment variable/property so on heroku we can for instance just change the env variable of the instance instead of having to make changes to the cbioportal repo's pom file. The latter will then only have to be done at the final stage when we deploy officially.

[jjgao]

@inodb I have mixed feelings about this. On one hand, it's a good idea to free frontend from backend. On the other hand, the frontend is still tightly connected to the current portal and core modules. Only specific versions of portal-frontend and portal can work together. For the moment, I think it may be still better to check in the frontend version into a file (not necessary pom.xml though).

Once we discard the portal and core modules and the API is more stable, we can decouple the frontend. We still need to find a way to specify which API version is working for which frontend version.

[inodb]

@jjgao I think it would be very useful for review on Heroku at the moment. Currently we do the same thing during development using our localDev=true trick, but it's more tricky to share a URL, since you have to make changes to the pom file on the backend. It would for the start just be for internal development use.

If we are going to expand the use of this feature to other portal maintainers I agree that it would be better to first have better warning messages when the frontend & api mismatch.

[jjgao]

@inodb maybe in addition to the checked in version, we can support it in props file (which overrides the checked-in one)? We don't have to document it in order to keep it just for dev purposes for now.

[inodb]

@jjgao yes, exactly