Add gas deduction for encrypted tx execution

[p0p3yee]

1. Add gas deduction for encrypted transaction execution

GasUsed is estimated by using SimCheck() function

GasUsed * GasFee will be deducted before executing encrypted transaction, proceed if successfully deducted, revert otherwise.

2. Add test for gas deduction

3. Fixed Tx signed from binary can not be decoded in Pep module begin block

Closes #24

[bowenyou]

Please add a note as to the fact that we are only executing the first message in an encrypted transaction