Implement new shield collateral provision reward

[yoongbok-lee]

Summary

Add parameters to distribute parts of the block reward to the shield collateral providers.

Proposal

Use the non-linear model

/* The non-linear model:
 *         c+n                        l        d
 *   r = -------- ( a + 2(b - a) * ------- + -----)
 *        c+n+d                     l + L     c+n
 */

Where a and b can vary between 0~0.5.
d is the staked tokens for purchase
c is the total collateral
n is bonded but not collateralized tokens
L is the maximum shield leverage (currently 1)
l is the current leverage
r is thedistribution ratio from the block reward

Alternatives

Additional context

Groundwork for shield 2.0

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