Code cleanup and README improvement

[warpech]

• removed unused imports
• removed an empty file
• add information about expected installation and build times
• improve and consolidate the information about testing

[github-actions[bot]]

File size report: ( 6bd83108eaafeeb06af9c4c497ad5beb9673bc25 )

# HTML file sizes
-rw-r--r-- 1 runner docker 348K Oct 21 14:56 dist/sv/index.html
# JS bundle sizes
-rw-r--r-- 1 runner docker 1.3M Oct 21 14:56 dist/sv/legacy.vendors~embedsChartRenderer.6050bfd4ce62d5bdf3ae.chunk.js
-rw-r--r-- 1 runner docker 1.3M Oct 21 14:56 dist/sv/modern.vendors~embedsChartRenderer.c2a5c12c15d5c86b9457.chunk.js
-rw-r--r-- 1 runner docker 1.2M Oct 21 14:56 dist/sv/legacy.legacy.worker.57f1d5e50bb4936066d7.bundle.worker.js
-rw-r--r-- 1 runner docker 1.2M Oct 21 14:56 dist/sv/modern.modern.worker.0ab37b52ef495ce6d89c.bundle.worker.js
-rw-r--r-- 1 runner docker 544K Oct 21 14:56 dist/sv/legacy.SpreadsheetViewer.b3623b6f8b9c24e611ea.chunk.js
-rw-r--r-- 1 runner docker 397K Oct 21 14:56 dist/sv/legacy.main.8b1b2da3004a3f18d297.bundle.js
-rw-r--r-- 1 runner docker 394K Oct 21 14:56 dist/sv/modern.SpreadsheetViewer.22379fe548acb7f93a1a.chunk.js
-rw-r--r-- 1 runner docker 347K Oct 21 14:56 dist/sv/modern.main.4b37d1fe84c56e9618ce.bundle.js
-rw-r--r-- 1 runner docker 122K Oct 21 14:56 dist/sv/legacy.vendors~CrashScreen~SpreadsheetViewer.a6ed38d76b64bc7a8769.chunk.js
-rw-r--r-- 1 runner docker 122K Oct 21 14:56 dist/sv/modern.vendors~CrashScreen~SpreadsheetViewer.8ca49bc3d3f93e353a54.chunk.js
-rw-r--r-- 1 runner docker  72K Oct 21 14:56 dist/sv/legacy.vendors~SpreadsheetViewer.cb7deb4a7318962fb759.chunk.js
-rw-r--r-- 1 runner docker  72K Oct 21 14:56 dist/sv/modern.vendors~SpreadsheetViewer.c88a22625e49026e7505.chunk.js
-rw-r--r-- 1 runner docker  27K Oct 21 14:56 dist/sv/legacy.CrashScreen.8e8156eab6a03bd4926f.chunk.js
-rw-r--r-- 1 runner docker  23K Oct 21 14:56 dist/sv/modern.CrashScreen.e1fb7537a0b82eb8e087.chunk.js
-rw-r--r-- 1 runner docker  13K Oct 21 14:56 dist/sv/legacy.embedsChartRenderer.cb7e5304a90d22c0f2bd.chunk.js
-rw-r--r-- 1 runner docker 8.3K Oct 21 14:56 dist/sv/modern.embedsChartRenderer.073961864854d4803a45.chunk.js
# CSS bundle sizes
-rw-r--r-- 1 runner docker 31K Oct 21 14:56 dist/sv/SpreadsheetViewer.9e038aabc7f9bfa77853.extracted.chunk.css
-rw-r--r-- 1 runner docker 19K Oct 21 14:56 dist/sv/dark.8f9746538022b0f2fc5f9c97ee20197d.css
-rw-r--r-- 1 runner docker 19K Oct 21 14:56 dist/sv/light.03ddf3efe02cef7120efa35f2a51850c.css
# Total size of HTML files, CSS bundles and JS bundles
7.5M    total