128 - Extract OSS SDKs from the core library

[VincentKobz]

• extract every OSS SDKs scanner providers from the core library (enioka_scan).
• update the documentation to follow new changes.
• fix the demoscannerapp to include new scanner providers in the gradle build.

#128

[DaSpood]

Some scanner providers seem to not be properly instanciated in the demo app:

• GsSppScannerProvider
• HoneywellOssSppScannerProvider

With the following error/warning in the logs:

Could not instantiate provider - usual cause is missing SDK from classpath
java.lang.ClassCastException: com.enioka.scanner.sdk.honeywelloss.spp.HoneywellOssSppScannerProvider cannot be cast to com.enioka.scanner.api.ScannerProvider
at com.enioka.scanner.LaserScanner.discoverProviders(LaserScanner.java:106)
at com.enioka.scanner.LaserScanner.discoverProviders(LaserScanner.java:73)
at com.enioka.scanner.service.ScannerService.initProviderDiscovery(ScannerService.java:176)
at com.enioka.scanner.service.ScannerService.onBind(ScannerService.java:132)
at android.app.ActivityThread.handleBindService(ActivityThread.java:5128)
at android.app.ActivityThread.-$$Nest$mhandleBindService(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2514)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loopOnce(Looper.java:230)
at android.os.Looper.loop(Looper.java:319)
at android.app.ActivityThread.main(ActivityThread.java:8893)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:608)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1103)

Also the option for intent scanners is still missing from this version due to the lack of allowIntentDevices option (ScannerServiceApi.EXTRA_SEARCH_ALLOW_INTENT_BOOLEAN extra) in the default settings. IIRC you found the cause of this problem while working on the next task, it would be better to include the fix in this PR to ensure all SDKs are reachable: add a toggle for this option in the demo app's settings.