Merge the LFortran and LPython websites

[certik]

Currently we have two separate websites:

• https://dev.lfortran.org/ (just LFortran)
• https://www.ubaidshaikh.me/lcompilers_web_frontend/lpython (LFortran and LPython)

We should merge them into just one source repository and one effort. We can still deploy one at https://dev.lfortran.org/ and one perhaps at https://dev.lpython.org/, and each can have a different default language, but I think we should just maintain one repository and add options to select and make it easy for people to deploy.

As we have more frontends, we'll add more frontends.

I can see some features being enabled only for some frontends. But it seems most features are 100% identical to all frontends.