Android: Update QSslSocketPrivate::fetchSslCertificateData()

Replaces the raw jni calls with our own jni wrappers. This allows us
to make use of the centralized cache, avoid global data storage and
use a more optimized way to attach to the jni environment.
This change also removes the JNI_OnLoad() function since it's not
used. If we need to add a JNI_OnLoad() function later, we should find a
more suited place for it.

Change-Id: Id84ead10c27d03d19c160304b1f9853b381a103c
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Android: Simplify the jni code in QAndroidPlatformServices

Remove the use of QtAndroid::AttachedJNIEnv and lazily cache
the openURL() methodID on first use.

Change-Id: I601d13bc7d644d7cb2f78655ad40c7d9566cf3cb
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Android: Simplify the jni code in QtAndroidClipboard

Let the QJNI classes manage the jni environment and cache the jni
handles. This lets us lazily cache the jni handle until we actually
need them.

Change-Id: Iced91e7cab19bdcab8581e94c6f2dd766fed47ed
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>