Polish whitespace and imports

As part of pull request #179, commits 0d922e1, 003249c and d099100
introduced use of Java 8 language features and APIs. Commit c95f5ea
manually reverted these changes (see #184 as to why), but in the process
re-introduced formatting issues originally cleaned up by other commits
in #179. This change fixes those formatting issues.

 - Replace leading tabs with spaces (for reasons detailed in 0827fb5)
 - Add space before opening curly brace
 - Optimize imports using shared .idea/codeStyleSettings.xml (note
   especially expansion of wildcard imports. See rationale in 780393d)
 - Do not align assignments on equals sign
 - Remove unnecessary additional newlines
 - Remove braces from single-line loops and conditionals
Restore JDK 8 source compatibility in ethereumj-studio

This partially reverts commit c95f5ea, restoring use of Java 8 language
features and APIs to ethereumj-studio, while leaving etherumj-core
pinned to the Java 7 language level for Dalvik compatibility reasons.
For further details, see the prior commit and
https://github.com/ethereum/ethereumj/commit/c95f5ea#commitcomment-9119435.
Publish core artifacts continuously via Travis CI

The Travis CI build now publishes ethereumj-core artifacts (classes,
sources and javadoc jars) on every push to master. See updated
ethereumj-core/README.md for details. Note that the `gradle release`
task has been renamed to `gradle publish`.
Re-enable publication of coverage reports

Prior to this commit, jacoco coverage report XML files were not actually
being written to disk, meaning that the Gradle coveralls plugin had
nothing to publish to https://coveralls.io/r/ethereum/ethereumj. HTML
reports are now being written as well, for convenient local browsing.