JS: Parenthesize arguments of raw expresions

[marzipankaiser]

Fixes #505 by parenthesizing the arguments of RawExprs unless they are already atomic expressions.

Also tries to add few parentheses into the generated code.

[marzipankaiser]

Future work:

• [x] Double-check whether we need to parenthesize objects or literals in certain places.
• [ ] Delete double-parens in stdlib (hotfixes from earlier).

[marzipankaiser]

Future work:

• [x] Double-check whether we need to parenthesize objects or literals in certain places.

Update: You were right btw, that the receiver in a method call has to be parenthesized even if it is an object or number literal (but it seems to work for arrays).