Move Copying of Assets to Precompile Task

[aaronskiba]

Fixes #3493

Changes proposed in this PR:

• Moved the code for copying Bootstrap glyphicons and TinyMCE skins from the initializer to a custom Rake task.
• Created a new Rake task assets:copy to handle the copying of necessary files.
• Ensured that the assets:copy task runs before assets:precompile by setting it as a prerequisite.
• This change prevents the files from being copied every time the Rails application initializes (e.g., when starting the server or console), and only copies them during the asset precompilation process.