prevent installing Spring Tools into non-compatible Eclipse platform installs

[martinlippert]

Even though the marketplace entries for the Spring Tools have designated entries for specific Eclipse versions, you can still see and try to install the marketplace entry with older Eclipse versions, too. Often tines, this leads to a dependency issue at install time, which his hard to understand and difficult to explain to users.

Another issue might appear if users update their Spring Tools installation inside of their existing Eclipse installation to newer versions without upgrading to the latest Eclipse version. This might also lead to dependency or compatibility issues while installing or even later at runtime.

There are two things we need to look into:

• how can we configure the marketplace entry to not show up anymore for older Eclipse versions
• how can we prevent upgrades and installations of Spring Tools versions into older, non-compatible Eclipse versions