Add scroll bar for ChromoMap plot

[hoelzer]

One can change via sed or awk the following line from

<div id="htmlwidget-f6c6b982908bd2088de7" class="chromoMap html-widget"    style="width:960px;height:500px;">

to

<div id="htmlwidget-f6c6b982908bd2088de7" class="chromoMap html-widget"    style="width:960px;height:500px;overflow:auto;">

Thus, we don't need to reduce the number of plotted contigs or split them. Compare also with implementation in WtP.

[hoelzer]

ChromoMap is also implemented here which might help for adjustments