Modularise bugsnag-android into JVM, NDK, and ANR artefacts

[fractalwrench]

Goal

The current version of bugsnag-android includes JVM, NDK, and ANR error detection by default. We should modularise these into 3 separate artefacts, so that it's possible for users to exclude code/resources they do not use from their APK.

This should be an invisible change to anyone using bugsnag-android and bugsnag-android-ndk.

Changeset

• Created 3 modules which publish a JVM, NDK, and ANR artefact
• Created bugsnag-android and bugsnag-android-ndk module which publish the artefact intended for public consumption
• Updated CI/mazerunner to install to mavenLocal rather than copying AARs
• Updated contributing/readme instructions to account for new artefact structure
• Removed AAR size badge
• Altered ProGuard rules to retain BugsnagPlugin implementations
• Extracted shared gradle logic for library projects (e.g. lintoptions) to root-level build.gradle
• Disabled NDK crash detection by default for all artefacts
• Updated example app to use mavenLocal rather than compiling module directly, as this was somewhat error-prone in location SO files
• Migrated ANR code to separate module and SO file
• Add an publicly accessible BugsnagPluginInterface that allows for registration of plugins
• Create plugins for ANR + NDK module using BugsnagPluginInterface, which the Client attempts to load if the right Configuration option has been set

Tests

Installed the artefacts into a local maven repository, and tested:

• depending on bugsnag-android allows JVM, NDK, and ANR errors to be captured
• both bugsnag-plugin-android-anr and bugsnag-plugin-android-ndk can be excluded from the APK if their respective configuration options are disabled
• When ANR/NDK detection are disabled using the bugsnag-android dependency, no shared libraries are loaded (improves init time from around 80ms to 50ms on a Nexus 5x)

Remaining work

• The following bugsnag gradle plugin needs to be merged for SO files to be extracted from the new AARs. For review purposes, this can be installed locally. Update plugin to search for shared object files in new artefact locations bugsnag-android-gradle-plugin#168
• The artefact pages need to be setup on Sonatype/Bintray.
• We may want to consider smoke tests to verify that when the ANR/NDK artefacts are excluded, Bugsnag still initialises.

[kattrali]

I mostly follow so far, and the changes make sense though with some naming questions:

• Is bugsnag-android-ndk going to be published? If so this is a fairly significant break. If not, then bugsnag-android-ndk could continue to be an alias for bugsnag-android.
• Were other naming conventions considered, like having a bugsnag-plugin-* namespace for the plugin artefacts? That would resolve the above point and separate reporting libs from plugin libs.

[fractalwrench]

As discussed I will adapt this PR to do the following:

bugsnag-android: meta package that depends on all 3 artefacts
bugsnag-android-ndk: meta package that depends on all 3 artefacts (identical to bugsnag-android)

bugsnag-plugin-android-jvm: JVM exception handling
bugsnag-plugin-android-anr: ANR detection
bugsnag-plugin-android-ndk: NDK handlers

[kattrali]

As a general point of organization, what happens if someone excludes the "jvm" plugin because they only want NDK and/or ANR reporting? It seems like the core constructs of error/session reporting are in the JVM plugin, but it may be a misunderstanding.

[kattrali]

The modularization split looks good. I got a bit further into the implementation of the plugins and added a few questions.