Large re-organisation of the package to make it more coherent.

- packages similar to tasks or instruments should implement the manager and everything related to it in a manager package and put the base modules at the root (see tasks).
- preferences, state plugin now have their own packages in utils.
- log_system is now under utils as log
- the starting_log command now takes an optional arg to prevent capturing stdout and stderr, the -s commandline argument can be used to start in this mode.
- dependencies previously administered from the task manager now have their own plugin under utils/dependencies.
Minor fixes.
Fix LoopTaskView.
Fix editor selection after loading a measure.
Fix error display dialog. (and remove enaml warning).
Fixing some bug in the PNA tasks and pna driver.
Merge pull request #5 from bhuard/Fix_PNA

Fixing some bug in the PNA tasks and pna driver.
Fix issue when displaying warnings.
Fix minor issue in set_dc_voltage_task.
Fix minor in Looptask where the task database entries where not correct when the task was created with a child task.
Add a ArrayFindValue task.
Add a LoadArrayTask with a CSV interface.
Fix bugs in the execution editor and some ui quircks.
Fix resuming a measure (syntax errors led to trying to call clear_cache not on driver but on dict).
Fix issue in base_instr_view leading to interfaces views not being displayed if the interface exists before the creation of the view.
Fix issue in loop interfaces leading to the 'value' entry of the database not being initialized during the checks.
Make load tasks smarter by detecting the header of the file during check if possible and if the user has not provided a list of columns.
Fix stupid error in base instr view (not all instr_task have interfaces.....)
Fixing wrong handling of loop task database entries leading to absurd message about monitor entry when loading.
Add a tolerance of 1e-12 to ArrayFindValueTask.