Added money Blueprint

Added $table->money() Blueprint.

Usage

/**
 * This will create a column with decimal data type, precision of 8 and scale of 2 and column name money.
 **/
$table->money();

/**
 * This will create a column with decimal data type, precision of 8 and scale of 2 and column name price.
 **/
$table->money('price');

/**
 * This will create a column with decimal data type, precision of 18 and scale of 2 and column name price.
 **/
$table->money('price', 18);

/**
 * This will create a column with decimal data type, precision of 18 and scale of 4 and column name price.
 **/
$table->money('price', 18, 4);