Add email support

This commit adds a new starter to auto-configure a MailSender when the
necessary classes are present and when the property "spring.mail.host" is
set.

The auto-configuration also accepts any arbitrary properties that
JavaMail might need using the "spring.mail.properties" prefix.

Fixes gh-1760

spring-boot-dependencies/pom.xml

@@ -300,6 +300,11 @@
 				<artifactId>spring-boot-starter-logging</artifactId>
 				<version>1.2.0.BUILD-SNAPSHOT</version>
 			</dependency>
+			<dependency>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-starter-mail</artifactId>
+				<version>1.2.0.BUILD-SNAPSHOT</version>
+			</dependency>
 			<dependency>
 				<groupId>org.springframework.boot</groupId>
 				<artifactId>spring-boot-starter-mobile</artifactId>
@@ -545,6 +550,11 @@
 				<artifactId>jms-api</artifactId>
 				<version>1.1-rev-1</version>
 			</dependency>
+			<dependency>
+				<groupId>javax.mail</groupId>
+				<artifactId>mail</artifactId>
+				<version>1.5.0-b01</version>
+			</dependency>
 			<dependency>
 				<groupId>javax.servlet</groupId>
 				<artifactId>javax.servlet-api</artifactId>