migrate from yangster to theia-blueprint

[duncdrum]

see theia-ide/yangster-electron#35

from what I can tell, yangster-electron is abandoned it does not seem to be maintained.

theia-blueprint on the other is. We should consider recreating this repo's content using the new template thingy

[adamretter]

Let's revisit this once we have CI, tests, and everything back in good shape