Table::getBy($conditions) method

Useful when searching by unique parameter (guaranteed or unwarranted). This would prevent spreading methods like:

	/**
	 * @throws CompanyNotFound
	 */
	private function getCompanyBySlug(string $companySlug): CompanyRow
	{
		$companies = $this->table->findBy([CompaniesTable::SLUG => $companySlug]);
		if (\count($companies) === 0) {
			throw new CompanyNotFound();
		}

		\assert(\count($companies) === 1);
		return \reset($companies);
	}

cc @dkurowski @jpudil