Memory leak when using Rpc server

**Describe the bug**
CServerRpc and CClientRpc/CServerRpc are created with "new" in main.cpp, but are never deleted.

**To Reproduce**
Run Jamulus with and without valid --jsonrpcport and --jsonrpcsecretfile parameters.
Use Visual studio's memory usage diagnostic tool to check the difference in memory usage at exit.

**Expected behavior**
Cleanup on exit.

**Screenshots**

**Operating system**
n.a.

**Version of Jamulus**
master @ 953f2b8a1ccab70d715a54cc730e05059ae140d6

**Additional context**

Start in main.cpp and inspect the CServerRpc and CClientRpc allocations made with new, then run Jamulus with and without valid --jsonrpcport and --jsonrpcsecretfile parameters. Use Visual Studio's memory usage diagnostic tool to compare exit behavior; done means the RPC objects are cleaned up on exit without introducing regressions.

Written by the indexing model from the issue text.