Improve huge folds performance

Hi all,

Looks like this PL is related to travis-ci/travis-ci#1340 and travis-ci/travis-ci#5

##### 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.
Adding DocumentFragment does not help in this case, because nodes we add with  _appendChild_ are already in DOM, so they are removed and cause re-rendering anyway.

##### Performance measurements
I've done measurements inside https://github.com/travis-ci/travis-web. 

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>

*With DocumentFragment: Profile (47721.987ms, 1792460 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>74.26%</td><td>35439.336ms</td><td>42403.392ms</td><td>3533.616ms</td><td>0.141ms</td><td>38649.96ms</td><td>
folds (line 28)</td></tr>
<tr><td>anonymous</td><td>27</td><td>3.67%</td><td>1750.26ms</td><td>1750.66ms</td><td>64.839ms</td><td>0.028ms</td><td>557.406ms</td><td>
app.js (line 9504)</td></tr>
<td>anonymous</td><td>22582</td><td>1.02%</td><td>484.991ms</td><td>484.991ms</td><td>0.021ms</td><td>0.016ms</td><td>1.505ms</td><td>
renderer (line 94)</td></tr>
</table>

*With parent removing: 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>