Create a new table to store the list of plugins with following columns:
- plugin key
- plugin file checksum
- last plugin modification date (last time checksum has changed)
- base plugin key (useful for custom rules plugins)
When server starts, during plugin loading we should compute plugin checksum and compare with previous one. If different, set last plugin modification date to the current date.
Migration: table is empty, when loading plugins if there is no entry in "plugins" table, add it and set modification date to the current date. It means when upgrading to SQ 6.6, all code analyzers will be considered as "updated" for next project analysis.