Adding a "link" CSS class and removing some duplicate CSS rules
Replacing <div id="playbutton"> with <div class="play"> and removing some obsolete CSS
Fix some minor HTML/CSS issues
Minor fix: change the email input to be a true HTML5 email input (rather than a generic text input)
Reinstate previously broken "Loading" spinner

Using a new spinner image (since we're not using the fancy buttons anymore, which is what the previous spinner image was intended for).
Add form validation layout and functionality

This adds the ability to highlight invalid fields, as well as include validation error messages in the login / create new character forms.

This also slightly adjusts the behavior when the Enter key is pressed (rather than simply switching focus, it will actually attempt to log in, and will print an error for the first missing field). If the focus is already set to the first missing field, this makes the Enter key more responsive (previously, pressing Enter would have seemingly done nothing in this case).

This also fixes #119 (while I was adjusting the CSS to make space for the validation error messages, I also made sure that the "Create" link fits within the container).
Minor refactoring for getting the play button and changing its state (enabled vs loading)

This doesn't have any functional impact, but will prevent issues later. There are technically two "play" buttons present on the page (though only one is actually visible), so this.$playButton was actually a set of two elements, instead of just one.
Show an error message in the login form when attempting to log in with an incorrect password (fixes issue #53)
Merge pull request #125 from sergkr/issue53

Fixes issue #53 (show error message when attempting to log in with incorrect password)