Setting to change node to connect to

[MrStahlfelge]

Some users experience problems to connect to the primary mainnet node when sending funds:

Failed to connect to 213.239.193.208:9053

It is not clear what exactly causes the connection problem, but a setting to specify another node (and Explorer) could help and is desirable for decentralization.

[MrStahlfelge]

Additionally to the new setting implemented in 198c6f4, two random known peers will be tried to connect to if connection can't be made.

[MrStahlfelge]

Since ports are sometimes blocked on networks, it makes sense to use the explorer proxy to submit transactions instead:

https://api.ergoplatform.com/api/v1/docs/#operation/postApiV1MempoolTransactionsSubmit

EDIT: Other node APIs are needed as well. A complete node should be exposed via https

[MrStahlfelge]

• every 24 hours: get list of connected peers and save 10 with restapiurl set, no duplicates (also take peer that was fetched from into account), save into prefs
• add way to choose a new node from the list on the connection settings screen
• on connectexception error screens, suggest to set an other node to retry
• also add this to desktop branch