Prevent encryption operations to use swap files

I believe many of the encryption operations that are being done in memory could reach the disk if any wallet/node uses any encryption function whilst having a full memory. This would result in passphrases and private keys reaching swap files on disk, making it possible to access them.

Some of the affected functions include: `generateNew` , `xPrvChangePass` in **Wallet.hs** and `encryptedKey`,`encryptedCreate`,`encryptedCreateDirectWithTweak`,`encryptedChangePass`,`encryptedSign` in **Encrypted.hs**

In summary ensuring that encryption functions are done in memory will avoid the posibility of passphrases/keys being leaked into the disk and therefore susceptible to be stolen. A possible solution would be using `mlock` in unix and `VirtualLock` in Win32, which locks some memory space and ensures that some operations will always be executed in memory.