fix overlapping value tracker texts by spacing them out

label height is still hard coded

fix FindQwt script for platforms where qwt qt5 version isn't called 'qwt-qt5'

also added check for Qt version of the found qwt library

symbol setting may not exist in loaded settings file

such as at first run, don't display error in this case

make buildable with Qt version smaller then 5.5

ubuntu 14.04 ships with qt 5.2 and this is a relatively small optimisation

fix symbol show settings not loaded at startup

'toggled' is emitted for 'setChecked', 'triggered' is only emitted when user
actually clicks something

removed dependency to qtcolorwidgets library

color selection is implemented with a qpushbutton and qcolordialog

simplified ascii parsing, in auto num channels won't change on error #39

also if a parsing error occurs all of the line is ignored

re-implemented functions made explicit
unnecessary line deleted

leaving numChannels implementation completely to actual reader
undone commit 'numChannels common in all readers, abstracted'

fix issue #15 snapshots not loading completely in some cases

I think this is a buffering issue caused by use of QFile.canReadLine function.
Note that loaded portion of the file was approximately 16k.

fix qtcolorwidgets to a working version

There has been some updates to build structure of the qtcolorwidgets. This is
the quickest way to get things working again. This should have been done in the
first place.

cache bounding rectangle instead of re-calculating at every reading

improves performance significantly for big buffers

don't allow xmin >= xmax

it breaks the plot because of newly implemented setrectofinterest

fix get version for the case that there is a mercurial repo but no tag

in such case hg returns "null" tag

add options to disable/enable symbols

also fixes symbols always shown in multi plot mode, issue #5