Landing page layout & text

[cooperlab]

List of changes:
-Make text and images active links. Remove links "Main" and "Picker" (see Issue #81)
-Replacement images
-Change order to "Region", "Cell", "Nuclear"
-Region text - Title "Region", text "Region based active learning with convolutional autoencoders."
-Cell text - Title "Nuclei", text "Cell based active learning with convolutional autoencoders."
-Nuclear text: Title "Nuclei (segmentation)", text "Cell based active learning using traditional nuclear segmentation and feature extraction."
-Standardize box sizes (height)
-Add "Resources:" list below image pages
-Add resources link to documentation
-Add resources link to publication (http://www.biorxiv.org/content/early/2017/05/19/140236, use linked text "M Nalisnik et al, Interactive phenotyping of large-scale histology imaging data with HistomicsML", doi: https://doi.org/10.1101/140236"
-Add resources link to source "Source code"

[slee172]

Resolved in #83