Override global variables with our branding

[dpordomingo]

required by #132

It solves the problem described by #132 (comment)

If it is merged, we will be able to override and use Apache Superset variables, as seen in this example.

I only detected the following three small issues, that could be solved in a separate PR:

• "extra" border in dashboard headers #229 "extra" border in dashboard headers
• Charts title is slightly bigger than the prev one #230 Charts title is slightly bigger than the prev one
• subtitles in the charts aside are slightly different than before #231 subtitles in the charts aside are slightly different than before

[se7entyse7en]

Why some of the variables defined here have not been moved?

[dpordomingo]

@se7entyse7en do you mean: "moved to ./variables-override.less"?

If so, I only moved to ./variables-override.less, those that:

• do not exist in ./cosmo/variables.less
• do override a variable from ./cosmo/variables.less

Why? because since we're already importing ./cosmo/variables.less, it's not needed to override it with the very same value → it would not be clear which ones are kept equal, and which ones are overridden.

[se7entyse7en]

Thanks!

[dpordomingo]

@ricardobaeta feel free to merge on your own, and solve the mentioned issues in separate PRs.
An alternative is that they're not real problems because I only detected them as "differences between old and new"

[ricardobaeta]

This is so awesome @dpordomingo :)

Now we can have clean, structured and adaptive code, easily understandable and extendable by the community. Having in mind a possible contribution to upstream to enhance Superset's branding capabilities I would only change the comment on .../cosmo/variables.less - line 889 - from // Load source{d} variables to // Load Custom Branding variables.

If you agree, please be so kind as to address this last change and merge ✨Thank you!

[dpordomingo]

@ricardobaeta your suggestion was addressed and merged into master, many thanks for your review

[dpordomingo]

I'd consider the contribution to upstream once I find the way to solve the caveats described in the causing issue.