new API to update bridgelines

Currently we're passing the bridge lines to onionmasq when we start it by calling Java_org_torproject_onionmasq_OnionMasqJni_runProxy.

In case the user changes the bridge lines while the VPN is already running we need a mechanism to update the bridgelines.

Similar to how it's done for the exit node country selection (Java_org_torproject_onionmasq_OnionMasqJni_setCountryCode a setter would be nice, that we can call, followed by a call to Java_org_torproject_onionmasq_OnionMasqJni_refreshCircuits to cause a refresh.

Otherwise we would have to start and stop the VPN, which might cause traffic leaks.