Dump all data to website in new format

[vorugantia]

@cdeil - This PR includes the following tasks:

• [x] Dump all cats to JSON using Gammapy (except SNRcat) and writing in new format
• [x] Dump each individual source into its own JSON file
• [x] Handle np.nan and np.inf values in Python data dump method
• [x] New directory structure
• [ ] Re-organize website to work with new JSON files, i.e. directory structure.

Have a look at the Python code in these commits so far. I will add another commit to this PR to finish the last checkbox above, but that will all be TS code. In the next PR, I will work on the source detail pages for each source.

The size of our data directory is large again, now that we're dumping all source data:

$ pwd
/mnt/c/Users/Arjun/github/gamma-sky/src/app/data/cat
$ du -sh *
26M     3fgl
6.8M    3fhl
72K     snrcat
1.1M    tev

[vorugantia]

The following has been done in the last couple of commits:

• [x] Move static data to src/data. Calling ng build will copy the static data over to the dist folder. (I tried putting the data in ./data but ng build wasn't copying the folder over to dist/. So now it's inside src/)

• [x] Have webpage access data from this new directory

• [x] Remove all static data from the master branch (add src/data to .gitignore)

• [x] Remove dist/ from the master branch

I'll merge the commit if this all looks OK, and if the tests pass.