Specan fixes

[fredzo]

Hi Andrew,

Here is the PR for specans:

• Adds rbw value to TimebasePropertiesDialog
• Adapts instrument properties in StreamBrowserDialog according to HasTimebaseControls() and HasFrequencyControls() values
• Adds missing PushIds that could lead to collisions when text/values were the same on two links.
  

A call to GetResolutionBandwidth() and GetCenterFrequency() is made in the render method of StreamBrowserDialog.
A PR will come on scopehal to make these methods cache the value for Tek driver (which is the only one that does not cache the value).

Best,

Frederic.