Fix OSK missing keys on older Android configurations

This fixes #304

Reference: https://jira.appcelerator.org/browse/TIMOB-16358

Older versions of WebView have an issue with transparent/gradient backgrounds. The symptom was the OSK slowly loading keys individually, and having the OSK be missing keys.

A workaround fix is styling the body `background-color` alpha to 1.0.

## Testing configuration
* Android API level 22
* Nexus One emulator
* French-French keyboard