Feature pyramid attention (FPA) modules

[daniel-j-h]

We should look into the feature pyramid attention (FPA) module for pixel-precise attention for segmentation features extracted from our resnet encoder.

Pyramid Attention Network for Semantic Segmentation
https://arxiv.org/abs/1805.10180

from https://arxiv.org/abs/1805.10180 Figure 2

from https://arxiv.org/abs/1805.10180 Figure 3

The GAU modules could be interesting to try out instead of our simple decoder modules, too.