Replace rakyll/static with native embedding

[Darkren]

Did you run make format && make check?
Yes
Fixes #703

Changes:

• rakyll/static was replaced with native embedding;
• make build-ui was modified to make use of native embedding.

[jdknives]

@Darkren good job overall. We need to bump Travis to Go 1.16, update the README and please answer my query above. Then this can go. Well done!

[Senyoret1]

I’m not sure about how the embedding procedure works, but it worked well in my test, so appart from my comments I don’t find any problems 👍

[Senyoret1]

I think having move-built-frontend here is a problem. With this, now the dist folder will have to be present every time anybody wants to build the binaries. As it was removed from the repo, that would mean the need to have all the front-end tools intalled and build the UI each time befor building the binaries, which would be inconvinient. Also, the process would be complicate even having the front-end tools, because make build-ui calls make move-built-frontend, which would remove the dist folder just after finishing, so a call to make build just after calling make build-ui would fail. I think the solution would be to remove move-built-frontend from here.

Maybe the same applies to build-static.

[Darkren]

@Senyoret1 agreed. but we definitely need dist in cmd/skywire-visor to build binaries now. native embedding requires that files being embedded are ready at compile time. I removed this command but left it in build-ui. so that built ui in the end lies where needed