Fixed repeat of backspace

The backspace command now properly checks the start option in the
backspace setting.  This required us defining the value of the insert
start point when not in insert mode.  There is no documentation for this
but it appears to be the caret point experimentally.
Fixed virtual space processing

VsVim now properly treats a blank line + virtual space as the vim
equivalent of autoindent.  A backspace which shouldn't delete the spaces
will no longer cause a buffer edit that inserts spaces.
Moved insert commands to actual commands
VS no longer custom processes Back

Visual Studio will no longer custom process the <BS> keystroke when
'softtabstop' is enabled.  At the point 'softtabstop' is enabled VsVim
knows more about <BS> handling than Visual Studio.  Hence custom process
is disabled and normal Vim semantics take hold
VS no longer custom processes Tab

Same reasons and logic as not custom processing back
Fixed tab handling
More unit tests