Better UI: add loading animation between page changes

[githyuvi]

@benoit74 Should I add a loading animation during topic/params change for a better user experience.

[benoit74]

It is not an urgent matter, but clearly a nice to have, so if you have something to propose, feel free to make a PR!

[yugalkaushik]

@githyuvi so i'm also contributing to this repo and i don't have an idea if i had setup the project correctly as zimui website is running but i don't think that is complete. So can you help me and also send a ss how it is appearing on your device.

[benoit74]

@yugalkaushik did you followed https://github.com/openzim/kolibri/blob/main/CONTRIBUTING.md#developing-the-zim-ui-in-vuejs (if so, please open a dedicated issue "how to develop the Vue UI" to not pollute this issue with irrelevant comments, even if the instruction seem enough and we can't always help on all developer setup).