resolve #2116 Sources with variable frequency

[AHaumer]

This is a resolution to fix #2116
Before doing that, I removed the "encapsulated" from 3 examples (don't know why that was used).
To implement the voltage and current source with the same icon, I moved the icons form the partial models to a new Icon package.
Implementation is robust. Parameter startTime omitted, since this affects the initial phase shift (which can be initialized anyway) and if the sine should start later, you could keep the amlitude to zero until the sine should start.
To test the sources, there are 2 new examples.

[beutlich]

Should the sources from Modelica.Electrical.Analog.Sources (for example SignalVoltage) also inherit from the new source icons?

[AHaumer]

@beutlich As far as I see, all sources inherit from partial VoltageSource or CurrentSource, and these inherit from the same icons. So the icons are defined only once.
The partial VoltageSource or CurrentSource cannot bs used for the new variable frequency sources, since the replaceable signalSource is of no use for variable frequency.

[christophclauss]

It is o.k. to me.

[AHaumer]

Just wait a little bit with merging,
I'll provide the signal source block, too.

[AHaumer]

Just wait an hour or two, I'll provide two nice examples.

[christiankral]

OK for me

[beutlich]

Two questions:

1. Why is only a new sine block added, but no cosine block?
2. Should SineVariableFrequencyAndAmplitude really go to Blocks.Sources, since it is the only block having inputs? Could also go to Blocks.Math.

[AHaumer]

@beutlich It's more a source. You may define frequency and amplitude constant, or prescribe them via inputs.

[AHaumer]

@beutlich There's also only an ExpSine, not ExpCosine.
With ExpSine you achie an ExpCosine by phase = pi/2.
In SineVariableFrequencyAndAmplitude you achieve a cosine by choosing the initial value of the angle (state).
BTW, may I propose a sinc-source (sin(x))/x ? It's important when dealing with signals ...

[AHaumer]

I've also improved the icon.

[AHaumer]

I've added cosine with variable frequency and variable amplitude