Move JS contents of bootstrap to main

The bootstrapping was done a separate file so the bootstrap could be
written in JSX. Since the code is extremely short, writing it in JS is
reasonable and removes the need for a separate JSX file.
Use a large modal for displaying app information

Modal sizes were added in Bootstrap v3.1 and give more space for the
heaps of info apps need to display.
Bind only to methods owned by task list component

React was raising an error because TaskListComponent was binding a
function it didn't own:

    bind(): React component methods may only be bound to the component instance.

Let TaskListComponent encapsulate the existence of the checkbox and call
props.onTaskToggle like the <tr> click does.
Add validation errors to new app form

* Addresses the problem from pull request #137 by making "cmd" optional
  if an executor and a container are provided.
* Validation logic taken from commit
  https://github.com/mohitsoni/marathon/commit/f61f2337290ec9921acb7f090582f0481855fa43