Fix: #2 NullPointerException when adding a variable
Fix: Exception appeared in the IDEA console, when calculate variables from templates. Moving it to the IDEA log

Fix NullPointerException which is described in the #2

• Change text field of variable's name to editable combobox with autocomplete
• Read all possible variables from all file templates via FileTemplateManager (compatible with all IDEA platform's products)
• Set all possible variables to combobox's list in alphabetic order
• Remove UPPER case validation, since we can define non UPPER case variable in the templates.

• New UI validation behavior:
  • Name should be in UPPER case
  • During rename variable new name should not be exists
• Small refactoring of the code

• Fixes issue with loading and saving Default Project's settings
• Rename title of "Template Variables" to "File and Code Template
  Variables"

First alpha release.