Rename some SVG identifers for clarity

[Ericson2314]

@samueldr OK I understand the layers in the snowflake better now. Sorry for the deluge of PRs, this one should be the safest and most conservative place to start. I'll rebase / reevaluate other things in order or increasing severity.

[samueldr]

No worries! And thanks again for taking time for this! These are all things I have gotten familiar with by playing around with stuff in here.

This PR is the right kind of improvement all around! While it won't matter much for editing with Inkscape, it will make things easier when doing things with the source.

Though, might I suggest naming them lambda-with-gradient-[dark|light]-X instead of lambda-gradient-[dark|light]-X; the gradients themselves have IDs, I initially thought that the lambda-gradient-... where the gradient references and not the lambdas themselves. What do you think of this?

Though I now see that in one file, one gradient identifier was changed, they weren't all changed, and not touched in other files. Was this done through grep/sed through the files for the known identifiers? Is there more work waiting for this PR?

(Yay bikeshedding where no one will see!)

[Ericson2314]

Hmm yeah everything is did there was repo wide sed.