Prereqs for further development; a more thematic notification sound; improve the OPRs list

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Summary:

• Update to current tools (without changing targetApi yet): Android Studio 3.1, build tools 27.0.3, gradle 4.4, android gradle 3.1.0, current repositories, compileSDK 26, JDK 1.8, remove Retrolambda, Android gradle DSL updates, newer support libs.
• Update to a more thematic notification sound It’s also higher pitch so it should be easier to hear from phone speakers.
• Don't show OPRs before there are any match stats.

Issues Reference:

Test Plan: It works on my phone.

Screenshots:

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BTW, I just guessed at the updates for .travis.yml.