StandardPanel bugs fixing

#### Purpose 

Fix bug with resizing of `StandardPanel`.
Fix bug with dragging class down.

#### Modifications

Hidden `StandardPanel` shouldn't be arranged in `LibraryWrapPanel.ArrangeOverride`.
Handle situation when `StandardPanel` is selected.

#### Additional references

[MAGN-5345](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5345).
[MAGN-5356](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5356).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.