User-defined JavaScript

[emmby]

Provide a mechanism for the user to specify optional JavaScript to add to the page without incurring all the overhead of switching to littlefs.

Example usage:

ESPUI.setCustomJS("window.onload = function(){ console.log('Hello world!'); }");

The JS is served up at /js/custom.js which is referenced from index.htm. custom.js is empty by default unless specified by the user.

Because the JS may be relatively long, the setCustomJS() function takes a const char* instead of a String& to avoid dynamic memory allocation.

Enables functionality such as emmby/WatchTower#10

[s00500]

this looks pretty sweet, is it ready for review yet ?

[emmby]

Yes, ready for review!

[s00500]

Nice! Thanks for your contribution