Trezor: session timeout improvements

Move session timeout from wallet to config
Prevent timeouts whenever a device operation is in progress
Move timeout job from each plugin to device manager

plugins/ledger/ledger.py

@@ -392,8 +392,4 @@ class LedgerPlugin(HW_PluginBase):
             wallet.proper_device = False
             self.client = client
 
-        if client:
-            self.print_error("set last_operation")
-            wallet.last_operation = time.time()
-
         return self.client