VRTK removes custom editor/property drawers

### Environment

* Source of VRTK (Unity Asset Store or GitHub).
https://github.com/ExtendRealityLtd/VRTK.git

* Version of VRTK (Unity Asset Store/GitHub release number) (GitHub master commit hash).
master #12df6d9

* Version of the Unity software (e.g. Unity 2018.3).
2019.1.0f2

### Steps to reproduce
I am using this inspector
https://github.com/SubjectNerd-Unity/ReorderableInspector
I uncommented ReorderableArrayInspector.cs
line 24 to turn all arrays into reorderable lists
line 27 to make all ScriptableObject fields editable

then after I install VRTK, those inspectors are no longer available

### Expected behavior
the inspectors from SubjectNerd-Unity/ReorderableInspector should be available

### Current behavior
those inspectors from SubjectNerd-Unity/ReorderableInspector are not available