Thonny

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* TECHNICAL: Changes in diagnostic logging

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* TECHNICAL: Implemented more robust approach for installing Thonny plugins

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* CHANGED: Installed plugins now end up under ~/.thonny/plugins
* TECHNICAL: Backend preparation now occurs when main window has been opened

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* FIXED: Backend related regression introduced in b8

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* CHANGED: (FIXED 231) Stop/Reset button is now Interrupt/Reset button (tries to interrupt a running command instead of reseting. Resets if pressed in idle state)
* FIXED 232: Ubuntu showed pip GUI captions with too big font
* FIXED 233: Thonny now remembers which view was on top in a panel.
* FIXED 234: Multiline support problems in shell (trailing whitespace was causing trouble)
* FIXED: pip GUI shows latest version number when there is no stable version.
* FIXED: pip GUI now can handle also packages without PyPI presence
* TECHNICAL: Backends are not sent Reset command for initialization anymore.

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* FIXED: Removed some circular import to support Python 3.4
* FIXED: pip GUI now also lists installed pre-releases
* EXPERIMENTAL: GUI for installing Thonny plug-ins (Tools => Manage plug-ins...)
* TECHNICAL: Thonny+Python bundles again include pip (needed for installing plug-ins)
* TECHNICAL: Refactored creation of several widgets to support theming
* TECHNICAL: THONNY_USER_DIR environment variable can now specify where Thonny stores user data (conf files, default virtual env, ...)