Fix color issue in dark theme

Abandon Nashorn and use Mozilla Rhino for JsPrettifier

Merge changes from PortSwigger

Some features (#33)

* Add line number for text editor using TextLineNumber;
Fix scroll issue

* Add remove segment button

Merge pull request #29 from nccgroup/zehuan-dev

Enhanced tab control and other fixes

Batch update (#27)

* Improve string concatenation performance

* Fix minor warnings

* Fix missing characters in HTML decoder

* Rearrange components; Add undo/redo functionality

* Add undo/redo to popup menus; Remove registered hotkeys that don't work

* Minor fix

* Higher undo limit; Clear data after tab is removed; Fix component view and other minor stuff

* Update README.md; Revert getMenuShortcutKeyMaskEx back to getMenuShortcutKeyMask to support Java before version 10

* Gzip decoder supports longer length of data

* Package re-structure 1

* Package re-structure 2

* Package re-structure 3

* Package re-structure 4

* Update error message logic

* Package re-structure 5

* Package re-structure 6

* Package re-structure 7

* Package re-structure 8

* Improve "Send to Decoder Improved"

Fix issue 16, non-UTF-8 is mostly supported (#26)

* Minor improvement on offset calculation

* Minor minor names

* HTML special char encoder supports non-UTF-8 chars now

* Re-org offset calculation

* HTML encode now supports non-UTF-8 characters; replace hard-coded "UTF-8" with `StandardCharsets.UTF_8`

* Allow non-UTF-8 characters in find and replace mode, if anything goes wrong, my bad

Update descriptions (#23)