UI: Adding new panel and extra buttons

[TimGoll]

To support more features / actions in the F1 menu, additional UI elements have to be added. This is a PR that aims to bring the elements to the panels:

This is a simple button that can have any action attached

These are two new types of buttons that can be added to many elemens. A "run" button that is basically a normal button that performs an action and a "toggle" button that toggles between states. Both can have any color or any icon, shown here are the default colors and states.

This is how these elements are added:

local form2 = vgui.CreateTTT2Form(parent, "new UI elements")

form2:MakeButton({
    label = "some label",
    buttonLabel = "this button is clickable",
    OnClick = function(slf)
        print("I was pressed")
    end,
})

form2:MakeCheckBox({
    label = "generic convar with two extra buttons",
    convar = "ttt2b_grenade_trajectory_ui",
    enableToggle = true,
    enableRun = true,
    OnClickToggle = function(button, state)
        print("toggling", button, state)
    end,
    OnClickRun = function(button)
        print("running", button)
    end,
})

form2:MakeCheckBox({
    label = "generic convar with two extra buttons number two",
    convar = "ttt2c_grenade_trajectory_ui",
    enableToggle = true,
    enableRun = true,
    toggleInitialState = 2,
    OnClickToggle = function(button, state)
        print("toggling", button, state)
    end,
    OnClickRun = function(button)
        print("running", button)
    end,
})

form2:MakeCheckBox({
    label = "only a toggle button!",
    convar = "ttt2c_grenade_trajectory_ui",
    enableToggle = true,
    OnClickToggle = function(button, state)
        print("toggling", button, state)
    end,
})

form2:MakeSlider({
    label = "a slider can also have one or two extra buttons",
    convar = "ttt_ironsights_crosshair_opacity",
    min = 0,
    max = 1,
    decimal = 1,
    enableRun = true,
    OnClickRun = function(button)
        print("running", button)
    end,
})

form2:MakeComboBox({
    label = "the same is true for combo boxes",
    convar = "ttt_crosshair_mode",
    choices = {
        { title = TryT("choice_crosshair_mode_0"), value = 0 },
        { title = TryT("choice_crosshair_mode_1"), value = 1 },
        { title = TryT("choice_crosshair_mode_2"), value = 2 },
    },
    enableToggle = true,
    enableRun = true,
    OnClickToggle = function(button, state)
        print("toggling", button, state)
    end,
    OnClickRun = function(button)
        print("running", button)
    end,
})

form2:MakeTextEntry({
    label = "textboxes are neat too",
    convar = "ttt_crosshair_mode",
    enableToggle = true,
    enableRun = true,
    OnClickToggle = function(button, state)
        print("toggling", button, state)
    end,
    OnClickRun = function(button)
        print("running", button)
    end,
})