Improve Streaming Enforcers getAvailableAmount function

[hanzel98]

What?

• The streaming enforcers needed an improvement in the function getAvailableAmount() to include the terms as an input, this allows to simulate the availableAmount before doing an initial transfer/claim.
• Changed the order of the function inputs to match other similar enforcers
• Added tests style improvements and new tests

Why?

• Before doing the first transfer/claim the allowance state is empty, and this provokes an error on the function getAvailableAmount, but adding the terms allows to estimate the available amount.