Fix bug overwriting scheduler/capture target name.

m_TargetName was being overwritten when the UI Element targetNameT was programmatically modified. This cause the signaling from the scheduler to capture to be missed (e.g. when targetNameT was set by reading a .esq file). This sets it so that m_TargetName is only overwritten when the user modifies the UI element, and not when it is changed programmatically.