Add skeleton states for different card components

[sebastinez]

To reduce the jarringness (what a word 😵) of the display and give the components a loading substitute I propose to replace Loading component in some specific places like the Landing page or the project listing of a seed node with pulsating skeleton cards, which are then replaced by the final loaded component.

Here an example video

https://user-images.githubusercontent.com/7912302/189319489-9244e86c-e0d6-4e6e-8584-b50df8c5d4f1.mov