i2ptunnel: Change enc type defaults

ECIES (ratchet) introduced about 4 years ago, and we are still defaulting to both ECIES and ElG in most places.

There are four cases:

- New install: $I2P/i2ptunnel.config as shipped
- New tunnel: i2ptunnel code sets default
- Existing tunnel, no enc type config: i2ptunnel code sets default
- Existing tunnel, config changed and saved via UI in last 4 years: Setting as in config file

Changes:

- New install: Change eepsite and IRC client to ECIES-only; shared clients remains both
- New tunnel: Change from both to ECIES-only
- Existing tunnel, no enc type config: Change servers to ECIES-only; clients remain both
- Existing tunnel with enc type config: No defaults, no change