Made the store backup clean up some of the older backups (> 7 days).

PlexRequests.Store/DbConfiguration.cs

@@ -23,6 +23,9 @@
 //  OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 //  WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 //  ***********************************************************************
+using System.Globalization;
+
+
 #endregion
 using System;
 using System.Data;