2.0.11-beta7

• Added support for negative focuses in Thermal lens and Thermal medium elements and in the GRIN Lens Assessment tool (#23).
• Added a tool for drawing simple lenses - Lensmaker.
• Can set custom offset inside range element for Round-trip Matrix function.
• Round-trip Matrix function can show matrices of all elements (optionally).
• New help topics in the manual: Round-trip Matrix function, Function freezing, Caustic function.
• Enabled HIDPI mode and fixed various related small issues (#15).
• Can use online documentation instead of local one (#9).
• Fix: schema table not properly updated after element deletion.
• Fix: there are no axis titles stored in example files.
• Fix: caustic window opens without axis titles.