Improve huge folds performance

Hi all,

##### Problem description
I've noticed that there is a performance problem in Firefox (both Windows and Linux) on pages like https://travis-ci.org/gark87/scalaz/builds/14647693.
As far as I understand, the reason is that modifying DOM (by _appendChild_) for every line in fold causes too many re-renderings.

##### Patch description
I've removed parent element before DOM modification, so its modification does not cause page re-rendering.
When all modifications are done parent element is put back.

##### Performance measurements
Using Firebug I've got the following statistics:
*Before: Profile (45300.839ms, 2053410 calls)*
<table>
<tr><th>Function</th><th>Calls</th><th>Percent</th><th>Own Time</th><th>Time</th><th>Avg</th><th>Min</th><th>Max</th><th>File</th></tr>
<tr>
<td>anonymous</td><td>12</td><td>72.4%</td><td>32799.981ms</td><td>37589.045ms</td><td>3132.42ms</td><td>0.191ms</td><td>34239.346ms</td><td>
folds (line 28)</td></tr>
<tr><td>anonymous</td><td>13</td><td>2.36%</td><td>1069.513ms</td><td>1069.711ms</td><td>82.285ms</td><td>0.029ms</td><td>542.088ms</td><td>
app.js (line 9504)</td></tr>
<tr><td>anonymous</td><td>22582</td><td>1%</td><td>451.817ms</td><td>451.817ms</td><td>0.02ms</td><td>0.015ms</td><td>0.137ms</td><td>
renderer (line 94)</td></tr>
</table>

*After: Profile (17760.342ms, 1839324 calls)*
<table>
<tr><th>Function</th><th>Calls</th><th>Percent</th><th>Own Time</th><th>Time</th><th>Avg</th><th>Min</th><th>Max</th><th>File</th></tr>
<tr><td>
anonymous</td><td>12</td><td>31.03%</td><td>5511.057ms</td><td>5518.998ms</td><td>459.917ms</td><td>0.16ms</td><td>3115.039ms</td><td>
folds (line 28)</td></tr>
<tr><td>anonymous</td><td>33</td><td>10.24%</td><td>1818.61ms</td><td>1818.89ms</td><td>55.118ms</td><td>0.028ms</td><td>539.406ms</td><td>
app.js (line 9504)</td></tr>
<tr><td>anonymous</td><td>22582</td><td>2.54%</td><td>450.867ms</td><td>450.867ms</td><td>0.02ms</td><td>0.015ms</td><td>0.119ms</td><td>
renderer (line 94)</td></tr>
</table>