Donate over proxy and password protection
### Donate
Default value for `donate-level` changed to `0`, it means proxy no longer take additional fee by default.

However added feature to allow xmrig miners donate over proxy if case if miners can't connect to donation servers directly (eg lacks of Internet connection on miner side). All donations fee taken from miners, not proxy.
If you prefer old legacy donation method, it still possible, just set non-zero value for `donate-level` option, this will disable new donation over proxy feature, but free threshold (was 256 connections) was removed.

⚠️ Be careful, if you use config from previous versions you must change value for `donate-level` option according information above.

### New options

* `"algo-ext": false,` Disable `algo` protocol extension (part of algorithm negotiation) to better compatibility, this can be used only if `donate-level` set to `0`.
* `"access-password"` Sets password for access protection, if this option set miners must provide valid password.

#### Miner side.
	
Added new option `donate-over-proxy` with 3 possible values:

* `0` Donate over proxy disabled, only direct connections allowed.
* `1` (default) Miner will try use proxy first with failback to direct connections.
* `2` Direct connections disabled.

### Compatibility
This features only supported in v2.15 (beta) for proxy and CPU miner, this version include many changes in code including real graceful exit. Code available in **beta** (stable beta release) and **evo** (current development) branches.
