Issues with switching backend in settings

[nondiremanuel]

Recently (#1241 (comment)) we introduced the possibility to switch from one node type to the other in the settings.
This is creating some issues, such the one signaled by @kloaec:

if I add a valid electrum node while already using bitcoind, it hangs Liana (it's an ssl node tho, mempool)

The idea would be to not give the switching possibility in v7 but addressing such issues in a followup

[jp1ac4]

Does it also hang if updating the Electrum address to this value from another or is it specifically related to switching node type?

[jp1ac4]

There should be less chance of hanging with Electrum connections after #1282.