Refactor the code of Dialog's UI view tabs toogling

[kdidenko]

See popup.js Lines: 4 - 27

instead of manually "switching off" all previously active tab and switching on the one required, and adding same code blocks for each new tab in the future, changed code must determine which tabs exist, which must be "off" and which to activate automatically

[kdidenko]

all functions with signature like:

function showSaveTab() {
	// switch tabs
        ....
}

must be replaced with a single function of

function showTab('Save') {
        ....
}