adds view menu item for downloads and history
`write_history` moved into utils
error shown in dialogs
busy cursor for loading shown
saving history from enter method, and downloads from download method
history read from inside the __init__ to provide current update in the list
changes button style to wxButton
adds clear history button in general preferences history box
adds `clear_list` method
adds finctions for calculating file size, writing history, and writing downloads
class for the downloads window
text file for saving history
updated