change the key from const char * to QByteArray

if trGettext() gets called with a *text that resides
in the stack, the QHash will return incorrect values after
the second call of trGettext() with that *text.

Example (assuming nothing has been translated):

void func(const char *text) {
        char *translated = trGettext(text);
        doSomethingWith(translated);
}

func("foo"); (1)
func("bar"); (2)

(1) *translated is "foo"
(2) *translated should be "bar" but is "foo" because
    the key (const char*) points to the value "foo"
    which has been set in the previous call (1).

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Replaced the tag implementation

The new implementation supports custom tags
which are provided by the user as well as
default tags which are provided by subsurface.
Default tags can be translated and will be written
to XML in their non-localized form.

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>
Added a custom widget for tagging dives

A custom tag widget has been added to MainTab.
Tags are seperated by a comma ",". The implementation
supports escaping a comma by using "\,".
While typing, the widget supports the user by suggesting
tags using a QCompleter.

Signed-off-by: Maximilian Güntner <maximilian.guentner@gmail.com>