Eliminate obsolete background data sync option

It only applied to pre-ICS devices.

ConnectivityManager.ACTION_BACKGROUND_DATA_SETTING_CHANGED is no longer
broadcast.

ConnectivityManager.getBackgroundDataSetting() always returns true.
Remove obsolete "Show unread count" preference

Only applies to pre-Honeycomb devices
Remove the obsolete "Condensed layout" preference
Remove AccessibleWebView

Only used on pre-ICS devices
Simplify ClipboardManager

No longer API dependent.
Remove com.fsck.k9.helper.NotificationBuilder

Only useful on pre-Honeycomb devices.
Remove code for unsupported API levels

An assortment of miscellaneous changes, each usually limited in scope to a
single file.
Increment settings version
Merge branch 'remove_obsolete_code'

PR #491 from zjw