fix(sqlite): refractor openDB() + added deleteDB()
feat($cordovaZip): add zip plugin

- adding the zip plugin from https://github.com/MobileChromeApps/zip
- docs coming soon

resolves #283
docs($cordovaZip): build
test($cordovaSQLite): add unit tests

add unit tests for `openDB` and `deleteDB` methods

waiting until #273 and 287
Merge pull request #288 from mrzmyr/test-sqlite

test($cordovaSQLite): add unit tests
Merge pull request #284 from mrzmyr/feat-new-plugin-zip

feat($cordovaZip): add zip plugin
Update README.md
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