make clicking terminology more consistent

Throughout plasma, "(left/middle/right/double)-click" is usually spelled with a hyphen, but not always; sometimes an un-hyphenated spelling is used. Sometimes a kcm or other dialog will even mix both spellings. Yet another form is "left button click"; distinguishing actual button presses from semantic actions makes sense with clicking emulations etc., but this use is not consistent. In addition, the touchpad kcm is not consistent about the use of clicking, tapping and pressing.

This change adds the hyphen to the uses of clicks and clicking actions, and separates clicking physical actions (e.g. "Press left and right buttons for middle-click"). Interacting with a touchpad is now called pressing when it involves the integrated button, never tapping. Additional labels are added to the radio buttons for the integrated right click menu indicating how to middle-click by pressing (only shown if the hardware does not support showing the separate middle-click configuration. The affected strings (and their control groups, if applicable) also have their translation contexts added or made more informative, and minor grammatical errors are fixed ("tap with two finger").