Lookup table for restore heights and a blockheight calculation function

Software wallets that use this library for 14 word mnemonic seed(s) may now use `seed->blockheight()` to obtain the Wownero seed blockheight (restore height) - previously, software wallets had to implement this functionality themselves.

include/wownero_seed/heights.hpp

@@ -0,0 +1,2 @@
+#pragma once
+unsigned int dateToRestoreHeight(time_t _t);

include/wownero_seed/wownero_seed.hpp

@@ -23,6 +23,7 @@ public:
 	std::time_t date() const {
 		return date_;
 	}
+    unsigned blockheight() const;
 	const std::string& correction() const {
 		return correction_;
 	}