Enable policy definition syntax to specify token 'end-of-life' rules

### Problem description
At present there are extensive facilities in the Policy language which can be used to mandate the 'beginning' of life - i.e. minting - of a token. There needs to be an equivalent capabilities for specifying the retiring rules of tokens.

### Requirements
Implement a definition language in the Policy allowing users to specify rules of retirement in the following way:
- retirement types: either one or the other or both - manual (no enforcement of matching) vs matched
- for the latter case there should be ability to define which policies' tokens can be matched with the ones issued by this policy, and at what matching rate (1:1, 1:2, etc)
- also facility to specify temporal dimension, i.e. which tokens (including the ones issued under the current policy) can be used in for retirements within which specific time period.

Support the above changes in the policy constructor UI and the policy file.

### DOD
- Policy definition language extended as per above
- Documentation updated to reflect the new capabilities
- Demo script update to reflect the capabilities

### Acceptance criteria
- Requirements above are addressed
- Policy engine correctly interprets the corresponding language contract
- Policy Constructor UI is updated to support this