Merge 'develop' branch. (Sandbox+Cabal, ...)
Merge last changes before 7.8 and lens branches
Catch all AsyncExceptions

Previously, only ThreadKilled exceptions were caught, the handler
pattern was inexhaustive. AsyncExceptions other than ThreadKilled are
rethrown now.

Cherry picked from bf80d72.
Correct boostrap takeover vulnerability
Reindent 'simple' section to 80 chars per line
Use more efficient dot file representation

Dotfiles can combine targets of common sources, so instead of

    A -> X
    A -> Y
    A -> Z

one can simply write

    A -> {X, Y, Z}

Which shrinks the dotfile line count by a factor of 5.7. In the future,
the drawing server will generate this format automatically; candidate
functions to do so have been introduced in

    c59eadc94ca7d10dbfad467ac8278ec010f4780e

already.
'Restarter' wrapper for node restarting actions
Refactor node pool

- Lens refactorings
- Introduce termination trigger newtype, instead of using MVar ()
  directly
Only 'Maybe' require termination trigger for node pools
Various small refactorings
Remove unused "connectToNode'"

This function behaved like "connectToNode", but did not close the
handles automatically.
Refactor lens TH
Add "Usafe" module again

The module provides a global counter, suitable for ad-hoc debugging.
Move client concurrency to the spawn site
Move Unsafe module to Utilities/
Merge changes from master branch

Conflicts: src/NodePool.hs (probably due to identical changes in
develop/master)
Small refactorings (mostly lens stuff)