Fix WebView Uri replacing

[renkun-ken]

What problem did you solve?

Closes #187

This PR fixes Uri replacing method in showWebView. It is made more robust to only replace non-protocol-specific Uri which points to a local file in htmlwidget source code. For example, in the following HTML tags, only paths starting with lib/ should be replaced with WebView resource Uri, and the last two should not be replaced since they are both protocol-specific Uri.

<script src="lib/htmlwidgets-1.5.1/htmlwidgets.js"></script>
<script src="lib/jquery-1.12.4/jquery.min.js"></script>
<link href="lib/datatables-css-0.0.0/datatables-crosstalk.css" rel="stylesheet" />
<script src="lib/datatables-binding-0.10/datatables.js"></script>
<link href="lib/dt-core-1.10.19/css/jquery.dataTables.min.css" rel="stylesheet" />
<link href="lib/dt-core-1.10.19/css/jquery.dataTables.extra.css" rel="stylesheet" />
<script src="lib/dt-core-1.10.19/js/jquery.dataTables.min.js"></script>
<link href="lib/crosstalk-1.0.0/css/crosstalk.css" rel="stylesheet" />
<script src="lib/crosstalk-1.0.0/js/crosstalk.min.js"></script>
<script src="data:application/javascript;base64,LyohIGhpZ2hsaWd6IlxcUyJ9fSk7"></script>
<script src="https://test.com/lib1.js"></script>

This fixes the handling of script tags created from base64 data uri.

(If you have)Screenshot