Implement missing bits in gas mechanics

[vaivaswatha]

In continuation to #12 , there are few things that still need to be implemented:

1. Support for gas_charge elements ListLength, DivCeil and LogOf. The latter two needs code generation in the compiler as well.
2. The interpreter scales the gas limit before beginning execution and later scales it back down. This should be performed in the VM as well (Scale down gas consumption scilla#877)
3. There are some fixed costs such as contract size + init file size charging during deployment, and message JSON size during transition execution that are missing in the VM.

[vaivaswatha]

4. Dynamic type check costs must be charged too. Note: This can't be done by introducing gas-charge statements in the transition body because the check must happen before the body executes, not potentially doing a lot of operations (and failing) before the gas charge statement gets executed. So it must be handled separately, as is done in the runner.

[vaivaswatha]

There are some fixed costs such as contract size + init file size charging during deployment, and message JSON size during transition execution that are missing in the VM.

This will be done by the blockchain code henceforth, to ensure uniformity b/w interpreted and compiled Scilla.