Make some usability improvements, especially in the Find Dialog

This MR:

• Makes some error / warning messages more clear
• Reformats the internet search button in the find dialog
• Reformats the major and minor axis display in the popup menu for DSOs
• Updates the docs on the popup menu
• Fixes a bug in the find dialog with object names (eg: NGC 1) which are substrings of many entries in the database (eg: NGC 100, NGC 1201, ...). This also fixes a bug where some objects in the observing wishlist would get incorrectly substituted by other objects!
• Prevents the user from searching the internet for an object that already is in the KStars database
• More proactively enables/disables the "OK" and "Internet Search" buttons depending on the situation
• Highlights the "Internet Search" button and the "OK" button depending on which action will be defaulted to by hitting Enter in the text entry