Android: Don't include Apache code under LGPLv2 license

The code which extracts style assets for the Android style
is licensed under the Apache license, which is not compatible
with LGPLv2.1. It is, however, compatible with LGPLv3. This
means that the Android platform plugin cannot be LGPLv2.1
as long as this code is included.

To minimize licensing confusion, we default to only providing
LGPLv3 for Android. If you want to build a LGPLv2.1-compatible
library, you can add -no-android-style-assets to the
configuration. This will in turn enable the LGPLv2.1 in
the configure output, and it will disable the extraction
code in the platform plugin.

Running the Android style with an LGPLv2.1-compatible platform
plugin will work, but it will look horrible.

[ChangeLog][Android] Default open-source license for
Qt for Android is now LGPLv3. For compatibility with the LGPLv2.1
license, add "-no-android-style-assets" to your configuration.

Change-Id: I6c7b52140f38138520871fa7c69debbb4ee90e6c
Task-number: QTBUG-41365
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Christian Stromme <christian.stromme@digia.com>