Use native font stack (#417)

[adamkudrna]

It ensures that the text is displayed in the font that the user is most comfortable with, and it also reduces the size of the data transferred.

Breaking change:

The Titillium web font has been replaced with native font stack.

Migration:

To keep the Titillium web font in your project, load the web font and override the --rui-font-family-base custom property:

--rui-font-family-base: 'Titillium Web', helvetica, roboto, arial, sans-serif;

Closes #417.

[bedrich-schindler]

I must admit that visually it looks cheaper now. Titilium font was good fit for React UI.

I am approving this anyway, but ... I am thinking about leaving note about fonts in README.md nad usage.md. You removed everything and I can imagine that people can be confused that there is nothing about fonts that I would expect. It can be link to foundation/typography.md, but I would consider leaving few words about fonts at those places.

I would also more encourage people to use Titilium (recommended by us for better visual experience) if they do not care much about network payload. But this is agains sentence This is a good practice because it ensures that the text is displayed in the font ... I think it is primary due to network.

To sum this up, previous commnets are just ideas and my notes to the problem. I am leaving them here so you can decide whether to change something or not. Overall result is expected .

[adamkudrna]

@bedrich-schindler I moved the font customization to the Customize section for better discoverability.

However, I don't the font is missing from the places you mentioned. I mean, I deleted it so it's missing now. But when you look at the docs as a newcomer, you don't have to think about the font until you actually want to change it. Then you head to the Customize section.