Allow a default prompt in the prompt widget

Closes #386
Option to invert mouse wheel commands for groupbox

The option allows mouse-wheel up and down to invert next/prev group
selection.

Closes #381
Fix a test

Due to 3474efca6496e8ff762811b4f35bb4b00b58365b this no longer raises an
exception. We should probably do something here (i.e. report command not found
or whatever), but it definitely shouldn't crash qsh.
Fix test

Looks like this was an accidental change in
9bab48c8debca6ac8371062e206c89e21514b112.
Remove all references to _abort

This is unused (it is not set anywhere any more) so we can delete it.
fix keyboardlayoutwidget
improved _Call.when() method

Improved when() method for floating window
Rearrange logic a bit
Changelog for 0.7++
Only have a version number in one place
Update install instructions

We don't need a source version of libxcb.
We can do better than forcing people to define a custom xsession.
Clean up installation process

* Use distutils instead of setuptools, since setuptools' find_package seems to
  ignore exclude, and we install the tests which is dumb
* Don't include a bunch of stuff in the manifest file that is unused
* manually install the battery icon resources
Version bump for Trusty Tahr
Fix ExtraFallback regression in configurable

Was broken by c8dbc66aee2df20a483582bd85ecc0dc50ebafc5
add GmailChecker textbox widget

Closes #392

Signed-off-by: Alexandr Kriptonov <alexandr.kriptonov@gmail.com>
Revert "Ensure WithdrawState windows stay unmapped on restart"

This reverts commit c8eda724dfabfa5288b56ffdd084a4765561813d.

There might (?) be a problem with this, so reverting temporarily before 0.7.0
is tagged.
Merge branch 'develop' into master
Release 0.7.0
Clean up documentation headers

Some day I will get all this right. Some day.
Correct a small mistake on README.rst