Gradle 7 / Java 16 build support

[jcxldn]

Most of the groundwork was laid out in #97.

Setting as a draft due to the pre-release nature of this PR.

Changes in this PR:

• Switched to gradle wrapper 7.0
• Added java 16 to CI matrix
• Remove duplicate lombok dependency (already provided by plugin)

Gradle 7 specific changes

• Remove jcenter() repository
• Add dependsOn to rootSources, copySubProjectJars and rootJacocoMergedReport to resolve gradle 7 implicit dependency warnings

Java 16 specific changes

• Switch to lombok edge-SNAPSHOT (awaiting formal tagged release, see [FEATURE] Make Lombok compatible with JDK 16 projectlombok/lombok#2681)
• Updated lombok for Java 16 compatability
• Add an --add-opens for :common:test to preserve FieldUtil functionality

[codecov]

Codecov Report

Merging #109 (0b6e6ad) into master (2afbdf2) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #109      +/-   ##
==========================================
- Coverage   34.51%   34.39%   -0.12%     
==========================================
  Files          63       63              
  Lines        2532     2532              
  Branches      286      286              
==========================================
- Hits          874      871       -3     
- Misses       1595     1597       +2     
- Partials       63       64       +1     

Impacted Files	Coverage Δ
...dumbdogdiner/stickyapi/common/util/StringUtil.java	91.13% <0.00%> (-3.80%)	⬇️

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