Bug 1105053 - Move LightweightTheme* to lwt/. r=vivek

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rename : mobile/android/base/LightweightTheme.java => mobile/android/base/lwt/LightweightTheme.java
rename : mobile/android/base/LightweightThemeDrawable.java => mobile/android/base/lwt/LightweightThemeDrawable.java