Move \int down among misc. symbols

Instead of at the top of symbols.js
Reorder LatexCmds/CharCmds registration for \prime #cosmetic
Fix LaTeX parsing of '

http://mathb.in/16257

It just being on CharCmds was a total mistake, it's a real LaTeX
command, we output &prime; as ', obviously we should parse ' as &prime;.

Technically in LaTeX it's a macro for ^\prime, so we shouldn't parse
\prime as being the same, but &prime; looks more like ^\prime (slash '),
so for now, just parse \prime wrong.
Move non-backslash-instantiated commands to top

...of symbols.js

(i.e. commands that can be typed without LatexCommandInput)
Add dollar sign symbol \$

Adds support for parsing \$; also makes it so that without
CharCmds.$ = TextBlock, typing $ will default to typing the
dollar sign symbol, \$.
Move VanillaSymbol and BinaryOperator to math.js

...next to Symbol, from symbols.js, because about to split up basic and
advanced symbols, but both depend on VanillaSymbol and BinaryOperator.
Split up symbols.js into {basic,advanced}Symbols.js
Separate out LatexCommandInput from commands.js

The rest of commands.js comes up in basic mathematics.
Merge branch 'api.no-auto-mathquill-ify' into feature.basic

So that test/visual.html can include both full and basic MathQuill
without them clashing
Fix empty math fields 0 width and height when created

Because the root block has .mq-hasCursor and no .mq-empty, because the
cursor is hidden but the root block wasn't blurred:
https://github.com/mathquill/mathquill/commit/a09f88f63617e05d6189889debceff4152aa36eb#commitcomment-6327135
Fix forgot to make new phony make targets .PHONYs
`make basic` builds mathquill-basic{,.min}.js

...which omit LatexCommandInput.js, advancedSymbols.js, and text.js.

Also, `make test` builds mathquill-basic.js too, so that unit.html can
include it and publicapi.test.js can unit-test it, and so that
visual.html can include it.

In basicSymbols.js, right after setting `LatexCmds.backslash`,
CharCmds['\\'] defaults to LatexCmds.backslash if LatexCommandInput.js
is omitted. (Note that the order of LatexCommandInput.js vs
basicSymbols.js when concatenated doesn't matter; even if basicSymbols.js
is first, LatexCommandInput.js just overwrites CharCmds['\\'].)

Closes #290, which is about configuring typing \ to insert \backslash.
Closes #306, which is about separating out commands that can only be
typed with LatexCommandInput; now separated as advancedSymbols.js.
Remove stix font from src
Fix ReferenceError when using mathquill-basic build

Test Plan:
Created a fraction without getting a JS error.