Reintroduce pgp-certificate-store layer

pgp-certificate-store/build.gradle

@@ -0,0 +1,36 @@
+// SPDX-FileCopyrightText: 2021 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+plugins {
+    id 'java-library'
+}
+
+group 'org.pgpainless'
+
+repositories {
+    mavenCentral()
+}
+
+apply plugin: 'ru.vyarus.animalsniffer'
+
+dependencies {
+    // animal sniffer for ensuring Android API compatibility
+    signature "net.sf.androidscents.signature:android-api-level-${minAndroidSdk}:2.3.3_r2@signature"
+
+    // JUnit for testing
+    testImplementation "org.junit.jupiter:junit-jupiter-api:$junitVersion"
+    testRuntimeOnly "org.junit.jupiter:junit-jupiter-engine:$junitVersion"
+
+    // Logging
+    api "org.slf4j:slf4j-api:$slf4jVersion"
+    testImplementation "ch.qos.logback:logback-classic:$logbackVersion"
+}
+
+animalsniffer {
+    sourceSets = [sourceSets.main]
+}
+
+test {
+    useJUnitPlatform()
+}