Move iconify to before setting alpha (#236)

[laggykiller]

This PR is written to solve #236.

Below is an exerpt from my response the issue:

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If self._toplevel is created with iconify=True, then execution is stuck until opening back the window. This is caused by src/ttkbootstrap/window.py Window.init and Toplevel.init:

# Function continue above...

if iconify:
    self.iconify()

# Function continues...

if alpha is not None:
    if self.winsys == 'x11':
        self.wait_visibility(self)
    self.attributes("-alpha", alpha)

# Function continue below...

Linux uses x11 display system. The Window/Toplevel was iconified before setting alpha, which causes wait_visibility() to get stuck until user open back the window. Hence, deiconify() in src/ttkbootstrap/dialogs/dialogs Dialog.build could not be called until user open back the window.

It seems like the visbility check is introduced by 2abfeb4 in response to #108 so removing that check is not an option.

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This PR would swap iconify() and set alpha such that alpha is set when 'visbible' before iconifying. Note that iconify() has to be called before self.transient(transient) to avoid error.