Integrate Spring Geode Logging with Spring Boot Logging and externalizes configuration.

* Deprecates the logback-include.xml file.
* Declare the logging context name as 'geodeLoggingContext'.
* Determines whether Spring Boot SLF4J Logback logging configuration (metadata) files are present on the application classpath.
* Applies custom logging configuration declared by the user in the spring-geode-logging.properties file on the application classpath.
* Conditionally includes SLF4J Logback logging configuration from Spring Boot.
* Includes Appenders, Loggers and Properties configuration metadata files from Spring Geode Starter Logging.

Resolves #117.

Author: jxblum

spring-geode-starter-logging/src/main/resources/logback-include.xml

@@ -1,4 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!-- DEPRECATED -->
 <included>
 
 	<appender name="console" class="ch.qos.logback.core.ConsoleAppender">

spring-geode-starter-logging/src/main/resources/logback.xml

@@ -1,12 +1,31 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <configuration debug="false">
 
+	<contextName>geodeLoggingContext</contextName>
+
 	<statusListener class="ch.qos.logback.core.status.NopStatusListener"/>
 
-	<include resource="logback-include.xml"/>
+	<define name="bootPresent" class="ch.qos.logback.core.property.ResourceExistsPropertyDefiner">
+		<resource>org/springframework/boot/logging/logback/defaults.xml</resource>
+	</define>
+
+	<include resource="org/springframework/geode/logging/slf4j/logback/properties-include.xml"/>
+
+	<variable resource="spring-geode-logging.properties"/>
+
+	<if condition='property("bootPresent").equals("true")'>
+		<then>
+			<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
+			<include resource="org/springframework/boot/logging/logback/file-appender.xml"/>
+			<include resource="org/springframework/boot/logging/logback/console-appender.xml"/>
+		</then>
+	</if>
+
+	<include resource="org/springframework/geode/logging/slf4j/logback/appender-include.xml"/>
+	<include resource="org/springframework/geode/logging/slf4j/logback/logger-include.xml"/>
 
 	<root level="${logback.root.log.level:-INFO}">
-		<appender-ref ref="console"/>
+		<appender-ref ref="CONSOLE"/>
 		<appender-ref ref="delegate"/>
 	</root>