Allow dynamic creation of search predicates using provider expressions

[Namoshek]

This PR introduces three new properties on the DataTablesColumn class:

• SearchPredicateProvider for SearchPredicate
• ColumnSearchPredicateProvider for ColumnSearchPredicate
• GlobalSearchPredicateProvider for GlobalSearchPredicate

Each of them can be used to create the respective search predicate dynamically using the search term as input. This is for example useful when receiving search input which needs to be transformed (e.g. tokenized, split, normalized, ...) before it can be used within the search predicate.

An example, as written in the README, which splits the search input to perform numeric range search, would be:

ColumnSearchPredicateProvider = (s) =>
{
    var minMax = s.Split("-delim-", System.StringSplitOptions.RemoveEmptyEntries);
    if (minMax.Length >= 2)
    {
        var min = long.Parse(minMax[0]);
        var max = long.Parse(minMax[1]);

        return (p, s) => p.Id >= min && p.Id <= max;
    }

    return (p, s) => false;
}