Refactor build system

The client was built with Meson, the server with Gradle, and were run by
a Makefile.

Add a Meson script for the server (which delegates to Gradle), and a
parent script to build and install both the client and the server to the
system, typically with:

    meson --buildtype release build
    cd build
    ninja
    sudo ninja install

In addition, use a separate Makefile to build a "portable" version of
the application (where the client expects the server to be in the
current directory). Typically:

    make release-portable
    cd dist/scrcpy
    ./scrcpy

This is especially useful for Windows builds, which are not "installed".

server/scripts/build-wrapper.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Wrapper script to invoke gradle from meson
+set -e
+
+PROJECT_ROOT="$1"
+OUTPUT="$2"
+BUILDTYPE="$3"
+
+# gradlew is in the parent of the server directory
+GRADLE=${GRADLE:-$PROJECT_ROOT/../gradlew}
+
+if [[ "$BUILDTYPE" == debug ]]
+then
+    "$GRADLE" -p "$PROJECT_ROOT" assembleDebug
+    cp "$PROJECT_ROOT/build/outputs/apk/debug/server-debug.apk" "$OUTPUT"
+else
+    "$GRADLE" -p "$PROJECT_ROOT" assembleRelease
+    cp "$PROJECT_ROOT/build/outputs/apk/release/server-release-unsigned.apk" "$OUTPUT"
+fi