Capitalize AmountMath but leave camelCase version for now

[katelynsills]

@dtribble suggested capitalizing AmountMath, since it is similar conceptually to Math. We will want to make sure that we leave the camelCase version amountMath for now, so that there are no breaking changes.

This task can be divided up into the following PRs:

• Introduce the new capitalized AmountMath and mark the other version as @deprecated
• Update documentation to the new capitalized AmountMath and mention the old version is deprecated
• Change all of agoric-sdk to use the new capitalized version (Change all of agoric-sdk to use capitalized AmountMath #3088)
• Change the dapps and any other known usages to use the capitalized version (Change the dapps and other usages to use capitalized AmountMath #3089)
• Eventually, a long time from now, remove the deprecated camelCase