css not cleared from previous layoutView

I'm submitting a bug report

* **Library Version:**
0.31.3

**Please tell us about your environment:**
* **Operating System:**
Windows 7

* **Node Version:**
6.11.4

* **NPM Version:**
3.10.10

* **Aurelia CLI OR JSPM OR Webpack AND Version**
CLI 0.31.3

* **Browser:**
all

* **Language:**
all

**Current behavior:**
when switching layoutView, previous css is not removed

**Expected/desired behavior:**
css should be removed

* **What is the motivation / use case for changing the behavior?**

this can be tested on this project (after logging in, among other things, bacground color #cccccc should be replaced). On page refresh all is OK (new color from other css kicks in).

https://github.com/bojanv55/aurelia-in-action

Start by reproducing the layoutView switch in the linked aurelia-in-action project after logging in, and observe which previous CSS remains applied. Done means the old CSS is removed when switching layouts so the replacement background color appears without a page refresh.

Written by the indexing model from the issue text.