Move the weighted gas price strategy under web3.tools

[pipermerriam]

related to #1463

What was wrong?

I believe that the weighted gas price strategy should be deprecated or moved to live under web3.tools. This is based on the high subjectivity of gas prices which I believe means that we will be unable to supply gas price strategies that work well across the many disparate use cases that Web3.py is intended for.

How can it be fixed?

The most extreme approach would be to deprecate and remove it. I'm not convinced this is the right choice.

I believe that the following course of action would be appropriate.

1. Move the weighted gas price strategy to live somewhere under web3.tools. This serves to designate this as not being part of the core library API, and thus to not be subject to as stringent of requirements for things like breaking changes.
2. Review our documentation around gas price strategies. Make sure that it is sufficiently informative so that someone could write their own gas pricing strategy that would serve their own needs.

[evowilliamson]

@pipermerriam Could you please assign this issue to me please ?

[pipermerriam]

@evowilliamson we don't really use assignees as part of our workflow. If you'd like to work on this you are welcome to simply open a pull request and mention this issue in the PR to link them together. Doing that is completely adequate for claiming an issue.

[evowilliamson]

@pipermerriam,

In his comment #1614 (review), @kclowes was suggesting refactoring the time_based_gas_price_strategy strategy, which is currently used both for the time and weighted strategy logic, into its own entity. Do you envision this issue (#1641) to be only effecting the weighted part of that strategy (kwarg weighted + code), or do you want to move the whole function to the web3.tools package and refactor it perhaps into two different strategies?