Vim: Tweak JS and JSX snippets

Just a small tweak to these snippets:

- Made "require" trigger "re" instead of "req" since the "q" key is so
  close to my snippet trigger key, typing this was awkward.
- Added "b" flag to some snippets because they should only triggered
  when they are at the beginning of the line.
Vim: Add "j" formatoption

According to Vim's help this option:

  Where it makes sense, remove a comment leader when joining lines.  For
  example, joining:
          int i;   // the index
                   // in the list
  Becomes:
          int i;   // the index in the list