Remove direct deps to boot in non boot modules

[isen-ng]

[INFO] +- org.springframework.shell:spring-shell-core:jar:2.0.0.RELEASE:compile
[INFO] |  +- org.springframework.boot:spring-boot-starter:jar:1.5.8.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot:jar:1.5.8.RELEASE:compile
[INFO] |  |  |  \- org.springframework:spring-context:jar:5.0.2.RELEASE:compile
[INFO] |  |  |     +- org.springframework:spring-aop:jar:5.0.2.RELEASE:compile
[INFO] |  |  |     \- org.springframework:spring-expression:jar:5.0.2.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-autoconfigure:jar:1.5.8.RELEASE:compile
[INFO] |  |  +- org.springframework.boot:spring-boot-starter-logging:jar:1.5.8.RELEASE:compile
[INFO] |  |  |  +- ch.qos.logback:logback-classic:jar:1.1.11:compile
[INFO] |  |  |  |  \- ch.qos.logback:logback-core:jar:1.1.11:compile
[INFO] |  |  |  +- org.slf4j:jul-to-slf4j:jar:1.7.25:compile
[INFO] |  |  |  \- org.slf4j:log4j-over-slf4j:jar:1.7.25:compile
[INFO] |  |  +- org.springframework:spring-core:jar:5.0.2.RELEASE:compile
[INFO] |  |  |  \- org.springframework:spring-jcl:jar:5.0.2.RELEASE:compile
[INFO] |  |  \- org.yaml:snakeyaml:jar:1.17:runtime
[INFO] |  +- org.springframework.boot:spring-boot-starter-validation:jar:1.5.8.RELEASE:compile
[INFO] |  |  +- org.apache.tomcat.embed:tomcat-embed-el:jar:8.5.23:compile
[INFO] |  |  \- org.hibernate:hibernate-validator:jar:5.3.5.Final:compile
[INFO] |  |     +- javax.validation:validation-api:jar:1.1.0.Final:compile
[INFO] |  |     +- org.jboss.logging:jboss-logging:jar:3.3.0.Final:compile
[INFO] |  |     \- com.fasterxml:classmate:jar:1.3.1:compile
[INFO] |  +- org.jline:jline:jar:3.4.0:compile
[INFO] |  \- org.jline:jline-terminal-jna:jar:3.4.0:runtime
[INFO] |     +- net.java.dev.jna:jna:jar:4.2.2:runtime
[INFO] |     \- org.jline:jline-terminal:jar:3.4.0:runtime

As Spring-boot-starter contains a lot of other dependencies that is not required by Spring Shell (eg, logging, auto-configure, etc). It should not be included in the core module. The core module should only do what the core module does (which is Spring Shell) and not include Spring Boot dependencies.

Instead the spring-boot-starter should be included in spring-shell-starter module instead as that is the start pack to simplify bootstrapping.

[fmbenhassine]

I created #1164 but I didn't see this issue. I agree, so I will plan this for the next major release.