sqbpro: Allow relative database file paths

When the path to the database file given in a project file doesn't exist
try parsing it relative to the path of the loaded project file. This
makes it possible to move project and database file around together
without need to manually correct the path in the project file.

See #36.
fix create table statements with IN operator

fixes issue #34
IN wasn't added to the token list and not enabled in the suffix expression
as this gives a parser generator warning, because of an ambiguity with IN as an operator
we stick with the warning right now
add a test with create table with IN
correctly extract check expression from AST
EditDialog: Use Monospace font in text editor
EditDialog: Fix text editor when NULL chars are typed in hex editor

When using the hex editor widget of the Edit Dialog to insert a NULL
character and then changing to the text editor without saving and
reopening the window first lead to the text being truncated at the NULL
character.
Fix bug in filter function when havin multiple filters

Since commit 707323067d62d7177a96418c8e1201297fc70d13 there has been a
bug in the SqliteTableModel::setQuery method which rendered the filters
useless when using them on multiple columns: Because this method is
called whenever a filter value is changed and because it deleted the
internal representation of the filters all filters except the one last
modified were deleted but still shown in the UI.
remove Ctrl+Return shortcut from executing sql

somehow neither F5 nor Ctrl+Return would work in that combination
edittable dialog: add splitter and better default size

I added a splitter and set better expanding properties
MainWindow: Add Ctrl+Return shortcut for executing SQL and add tooltips

Add the Ctrl+Return shortcut for executing the current SQL again. This
needs to be done using C++ code instead of setting it in Qt Designer
because setting multiple shortcuts in the latter means defining a key
sequence row.

Also add the keyboard shortcuts to the tooltips of the buttons as they
didn't appear anywhere in the program.
editdialog: accept shortcut for CTRL+Enter
Grammar: Parse NOT LIKE constraints correctly

Parse column constraints with a 'NOT LIKE' expression correctly. For
example in a table definition like this:
CREATE TABLE not_working(
    value TEXT CONSTRAINT "value" CHECK(value NOT LIKE "prefix%")
);

This fixes issue #40.
Tests: Add unit test for CHECK NOT LIKE constraint

Add a unit test for the grammar fix in
9cb0614ecfad1536c18e17061fa3aa48b26c1f68.
Tests: Make sure all unit tests pass

Two unit tests where failing because of missing spaces in the expected
result string.
MainWindow: Make it possible to cancel closing of database file

When closing the database, either by using the menu item or by closing
the window, the user is asked whether the changes he made shall be
saved or not. Add a third button to this message box which makes it
possible to cancel the action.
Ensure the Homebrew version of SQLite3 is found
Grammar: Fix parsing of NOT IN/GLOB/MATCH/REGEXP constraints

See issue #40.
grammar: cleanup expr and fix between suffix expression
grammar: add tests for like operator and between
Fix crash when sorting one table in the Browse Tab and changing to another

Fix a crash when sorting the n-th column of a table in the Browse Tab
and then changing to a table with less than n columns.