Allows creation of proposals that will revert once passed

[bbenligiray]

We can check if the proposal to be created will execute by using a VoidSigner that assumes the address of the respective agent the proposal is being made for. We do a .callStatic() call to check if it reverts, and display a warning message at proposal creation time if it does.

Note that this checks if the proposal would execute if it passed now, which may create some confusion. For example, say the agent has no funds. Knowing that it will be funded by the time my proposal passes, I attempt to create a proposal to transfer funds from it. Since the agent doesn't have these funds yet, the static call will revert and the dashboard will display a warning telling me that the proposal looks like it's going to revert. Here, I need to use my judgement and create the proposal anyway.

In general, I'm in favor of people creating proposals exactly and carefully. Hand-holding to this degree may result in people being even more careless about creating proposals or voting on them. Nah, this feature is needed.