i-bem: setMod should convert non-boolean value to string

[narqo]

block.setMod('blah', 2);
console.log(typeof block.getMod('blah'));  // number

block.setMod('blah', '2');
console.log(typeof block.getMod('blah'));  // string

Current behaviour looks weird and it seems that any value in the example above may fire several onSetMod-handlers (see buildModFnName()).

And the same goes to hasMod

[qfox]

👍