[MagicJoin] Allow the possibility to change the weight of individual keys or tables

[moufmouf]

If MagicJoin is using a wrong path because some part of it is known to be insignificant, it could be great if we were able to rate it.

For instance:

$magicQuery->setMagicJoinForeignKeyWeight($tableName, $columnName, $weight);

or

// All FK of this table or all FK pointing to this table will be multiplied by $factor
$magicQuery->setMagicJoinTableWeight($tableName, $factor);

[moufmouf]

Done via SchemaAnalyzer.