Support virtual sqlite3 tables in dbschema.json

Sqlite has two very useful extensions: Full Text Search and Spellfix search that could make searching on Zites more meaningful and very fast.

Looking briefly at files in src/Db, I think that it would be a very short change to enable virtual tables: One could just modify a couple of lines in the function createTable@DbCursor.py.

So a new virtual table using fts5 could be defined as

"fts_posts": {
    "virtual": true,
    "payload": fts5(title, body, uuid UNINDEXED)",
    "schema_changed": 1
}

that would be translated into CREATE VIRTUAL TABLE fts_posts USING fts5(title, body, uuid UNINDEXED). Update and delete queries works as in a standard table.

It is indeed true that such extensions are optional, but since ZeroNet ships with its built version of sqlite3 I think we can make sure such extensions are enabled.

Commencez dans src/Db/DbCursor.py au niveau de createTable, puis suivez la manière dont les entrées de dbschema.json parviennent à cette fonction. Confirmez comment le build SQLite fourni gère les extensions de tables virtuelles et vérifiez que le schéma proposé produit le comportement attendu de CREATE VIRTUAL TABLE, y compris les opérations de mise à jour et de suppression.