Add architecture selector and filtering

[ymartin59]

For new users, package views may be very different from Package Center.
I propose to add a "architecture selector", where Synology devices can be browsed, so that user can filter views to only relevant packages/versions available for its device.

Some ideas:

• Selector in header, defaults to "All architectures"
• JavaScript gets list of devices with architecture online - maybe from wiki page: https://github.com/SynoCommunity/spksrc/wiki/Architecture-per-Synology-model
• JavaScript sets a cookie with selected architecture name
• Packages list and package view restricts content to selected architecture if available in cooke