RFR: Added more labels

[Jesper Wilhelmsson]

* Added the labels: compilercontrol, conformance, footprint, jvmci
* Clarified where some features belongs
* Changed the html code slightly to make it easier to see the labels when scrolling up and down the file

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Commit messages:
 - Added more labels

Changes: https://git.openjdk.org/guide/pull/93/files
 Webrev: https://webrevs.openjdk.org/?repo=guide&pr=93&range=00
  Stats: 201 lines in 1 file changed: 54 ins; 86 del; 61 mod
  Patch: https://git.openjdk.org/guide/pull/93.diff
  Fetch: git fetch https://git.openjdk.org/guide pull/93/head:pull/93

PR: https://git.openjdk.org/guide/pull/93