feature(index): Provide a splash screen

It's ugly to show a blank white page for too long so we show a
reasonable default page ASAP. This page goes away as soon as
the JS/CSS needed has loaded so doesn't require user interaction
to get past it.

Closes #5
fix(header): make text white by default
chore(accounts): namespace accounts states
feature(forms): rename elggInputWrapper to elggFormField

BREAKING CHANGE: any uses of elgg-input-wrapper class must
be renamed to elgg-form-field. This was done because
Evan finds the name clearer and cleaner.

Before:
```html
<label class="elgg-input-wrapper">
```

After:
```html
<label class="elgg-form-field">
```
feature(accounts): update accounts forms to use elgg-form-field