Roles pallet Implementation

[salman01zp]

Summary of changes
Changes introduced in this pull request:

• Roles pallet implementation
• Implement RolesHandler trait for the pallet
• Implement bond and unbonding logic
• Add simple fixed amount slashing
• Add tests

Note:

Will add validator checks and re-staking logic in separate PR

Reference issue to close (if applicable)

Closes #280

[drewstone]

Looks great! Good start, I would like you to take a look at the jobs PR to ensure we're following similar style here on docs, comments, formatting, abstractions, etc.