Review MP bonus formula

[0x-r4bbit]

This was raised by @3esmit in #48 (comment).

Also, I didnt understand yet why the $MP_{bonus}$ is being calculated as it is.
Currently RewardsStreamerMP uses:

$$ MP_{bonus} = A_{balance} * \frac{\left(\frac{t_{locked} \times M_{MAX} \times {SCALE_{FACTOR}}} {t_{MAX}} \right)}{SCALE_{FACTOR}} $$

Why not use the normal formula?

$$ MP_{\text{bonus}} = A_{balance} + \left( \frac{A_{balance} \times t_{locked}}{t_{year}} \right) $$

Goal of this issue to analyze the impact of these two versions and making the changes if necessary.
There's also a chance we can stick with what we have, but right now it seems unclear.

[3esmit]

Just to help clear-up this formula, removing the $SCALE_{FACTOR}$:

$$ MP_{bonus} = A_{balance} + \left(A_{balance} \times \left(\frac{t_{locked} \times M_{MAX}}{t_{MAX}}\right)\right) $$

I found this simplification:

$$ MP_{bonus} = A_{balance} \times \left(1 + \frac{t_{locked} \times M_{MAX}}{t_{MAX}} \right) $$

However, I need to check if this simplification is doable in solidity.