Move AddonsTreeView to separate control

#### Purpose

1. Remove `ScrollViewer` of `AddonsTreeView`.
2. Move `AddonsTreeView` to it's own control.
3. Add instances of new control to `LibraryView` and `LibrarySearchView`.

#### Modifications

Created new control `AddonsTreeView`. Added instances of this control to `LibraryView` and `LibrarySearchView`.

#### Additional references

[MAGN-4969](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4969).
[MAGN-4954](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4954).

#### Reviewers

@aosyatnik, @Benglin, please, take a look.