Update Firebase icon from original icon

[why]
Improve legibility. The full icon is in fact a multicolor icon and the
design depends on being rendered in multiple different colors. That is
impossible for fonts. So we should probably use their flat (mono-color)
icon instead, which hints the different 'flaps' through gaps instead of
colors.

[note]
Both icons (the old and the new) contradict rules given by Firebase to
use the logo. But that can not be helped in a icon font, as we just have
one color of undetermined hue.

Signed-off-by: Fini Jastrow <ulf.fini.jastrow@desy.de>

src/svgs/firebase_nf.svg

@@ -0,0 +1 @@
+<svg width="512" height="512" version="1.2" xmlns="http://www.w3.org/2000/svg"><path id="icon" d="m133.5 311.2 35.46-228.1c0.5386-3.475 3.228-6.215 6.678-6.804 3.45-0.5887 6.889 1.106 8.539 4.207l38.12 71.56zm251.8 55.34-33.75-209.9c-0.5099-3.014-2.65-5.491-5.549-6.421-2.899-0.9294-6.071-0.1561-8.224 2.005l-212.9 214.3 117.8 66.38c7.397 4.15 16.41 4.15 23.8 0zm-95.72-183.2-27.28-52.19c-1.407-2.688-4.18-4.37-7.202-4.37-3.022 0-5.795 1.683-7.202 4.37l-119.8 214.7z"/></svg>

src/svgs/icons.tsv

@@ -122,7 +122,8 @@
 090		i_seti_error				error.svg
 091		i_seti_eslint				eslint.svg
 092		i_seti_ethereum				ethereum.svg
-093		i_seti_firebase				firebase.svg
+093		i_custom_firebase			firebase_nf.svg
+093		i_seti_firebase
 094		i_seti_firefox				firefox.svg
 095		i_seti_font				font.svg
 096		i_seti_f_sharp				f-sharp.svg