Update Package.php

Attribute keys were not displaying on the uninstall screen. There wasn't an error, they just didn't show.
Fix Redactor strings and translations

- Add customStyles text (for "Custom Styles" plugin)
- Translate "Remove Style" item
Fix translatable string

Translatable strings must be fixed, they can't contain concatenations and variable parts
image slider - adding edit mode placeholder, making modal jump down to freshly added entries, fixing stacking delete click events, and adding arrow sort functionality
removing unnecessary markup
Fix typo in Elemental attribute
typo in content.xml
removing lightbox.js from git
Merge branch 'master' of github.com:concrete5/concrete5-5.7.0
more work on blog
Merge pull request #582 from evancooper/master

Image Slider QC + Sorting
Merge pull request #583 from mkly/fix_exclude_attribute_typo

Fix typo in Elemental attribute
Fix a few things in editmode, and allow layouts to be dragged within it's containing area.

Most notable fix: editmode and area blocklist clear themselves out on rescan, this prevents pointers to blocks whose elements no longer exist.
reformat arrange_blocks class
Reformat page user_interface
Layout dragging completed.
Fix layout within layout editing.
tweaks to blog styles; adding picture tag support to content block
Merge branch 'master' of github.com:concrete5/concrete5-5.7.0
Merge pull request #586 from Remo/patch-7

typo in content.xml