Add support for Mission Logs using Logback

[HimanshuSahu31]

This fix exposes an endpoint to get log information for a mission under execution. I've used Logback implementation of Slf4j API to use appenders which will be able to filter required events and publish them to consumers. Information can be added to MDC just before the log event is sent and this information will be extracted by the appender.

WIP below tasks:

• Add javadoc
• Add Tests
• Evaluate and add more meaningful log statements to implementations of MissionExecutor, StrandExecutor and LeafExecutor. (Currently, I've handled MDC statements in SingleNodeMissionExecutor only.)

Fixes #20

[codecov]

Codecov Report

Merging #38 into master will decrease coverage by 3.68%.
The diff coverage is 6.55%.

@@             Coverage Diff              @@
##             master      #38      +/-   ##
============================================
- Coverage     48.07%   44.38%   -3.69%     
- Complexity      393      394       +1     
============================================
  Files            95      105      +10     
  Lines          1922     2102     +180     
  Branches        150      163      +13     
============================================
+ Hits            924      933       +9     
- Misses          973     1144     +171     
  Partials         25       25

Impacted Files	Coverage Δ	Complexity Δ
...a/io/molr/mole/server/main/DemoMolrServerMain.java	0% <ø> (ø)	0 <0> (ø)	⬇️
.../io/molr/mole/core/runnable/RunnableLeafsMole.java	0% <ø> (ø)	0 <0> (ø)	⬇️
...molr/mole/core/logging/publisher/LogPublisher.java	0% <0%> (ø)	0 <0> (?)
...rc/main/java/io/molr/mole/core/api/MoleWebApi.java	33.33% <0%> (-4.17%)	3 <0> (ø)
.../java/io/molr/mole/remote/rest/RestRemoteMole.java	85.18% <0%> (-6.82%)	10 <0> (ø)
...lr/mole/core/logging/LogAppenderConfiguration.java	0% <0%> (ø)	0 <0> (?)
.../io/molr/mole/server/rest/MolrMoleRestService.java	33.33% <0%> (-1.67%)	4 <0> (ø)
...mole/core/logging/consumer/LogConsumerFactory.java	0% <0%> (ø)	0 <0> (?)
...n/java/io/molr/mole/core/local/LocalSuperMole.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...o/molr/mole/core/logging/appender/LogAppender.java	0% <0%> (ø)	0 <0> (?)
... and 19 more

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[kaifox]

Hi Guys, I just looked through the 2 available branches concerning the logs ... It looks that we could try to keep this one and delete the other one ... Basing future efforts based on this could be ok (though still some work to do).