1. Introduced a new db table "db_version_history" to hal-default.db. The table contains a list of db version. Every version has some parameters:
- 'db-version' (int) - A db version number. table 'conf', key 'db_version' points to this.
- 'force-upgrade' (default:0) - If 1 then force the upgrade to this version
- 'clear-internal-aggr-data' (default:0) - If 1 then clear all internal aggr data before upgrade.
- 'clear-external-aggr-data' (defualt:0) - If 1 then clear all external aggr data before upgrade.
The db table 'conf', key 'db_version' has to point to the db version to upgrad to. Only forward upgrades are supported.
2. Modified HalContext to act accoring to the parameters in the new db table.
Former-commit-id: 19bd87ade3129f3fc0c51f0e1b94f71dc854d792
