TelemetryConfigurationFactory should be able to read numbers in hexadecimal format #551

Currently it is not possible for numeric properties in the configuration to use hexadecimal numbers. For example

<Add ProviderName="Microsoft-Windows-PowerShell" Keywords="128" />

works but

<Add ProviderName="Microsoft-Windows-PowerShell" Keywords="0x80" />

does not.

Using hexadecimal values is very convenient when the property represents some flags. We should support it.

The reason this does not work today is that TelemetryConfigurationFactory.LoadInstanceFromValue() method calls into Convert.ChangeType(), which does not support hexadecimal values. For numeric properties we should try harder. For example, if the value starts with 0x or 0X, we could attempt Int32.TryParse() with AllowHexPrefix set before falling back to Convert.ChangeType.